WO2009125741A1

WO2009125741A1 - Electrode catalyst for a fuel cell and method for manufacturing an electrode catalyst

Info

Publication number: WO2009125741A1
Application number: PCT/JP2009/057055
Authority: WO
Inventors: 小西　繁
Original assignee: 信越化学工業株式会社
Priority date: 2008-04-07
Filing date: 2009-04-06
Publication date: 2009-10-15
Also published as: JP2009252542A

Abstract

Disclosed is an electrode catalyst for a fuel cell, said catalyst obtained by growing a catalytic metal that includes platinum and ruthenium on a core of metallic microparticles, wherein the mean coordination number of a first neighboring platinum atom surrounding a ruthenium atom within a catalytic metal in the atmosphere that includes platinum and ruthenium is 3.5 or above. Compared to a commercial PtRu black catalyst, and a conventional PtRu-supported carbon catalyst created by using a trivalent Ru raw material, the fuel cell electrode catalyst has improved methanol oxidation activity per unit mass of the catalyst, and is stable, where the change in active surface area and methanol-oxidizing activity caused by a change in potential is small. By using the fuel cell electrode catalyst as the anode catalyst for fuel cells, a high-performance fuel cell can be provided.

Description

Fuel cell electrode catalyst and method for producing the same

The present invention relates to an electrode catalyst for a fuel cell, particularly a direct methanol fuel cell, and a method for producing the same.

In mobile phones, it is desired to increase the capacity of batteries, but it is difficult to increase the capacity of secondary batteries. For this reason, direct methanol fuel cells (DMFC) using methanol fuel have attracted attention.

Since DMFC can be used as it is without reforming liquid fuel to hydrogen, etc., it has advantages such as being able to be made compact, and is currently being intensively studied for practical application. However, high methanol permeability of the electrolyte membrane and low methanol oxidation activity of the anode catalyst are problems for practical use. Furthermore, when considering stable use for a long time, durability is also required.

A PtRu-based catalyst is mainly used as the anode catalyst, but since the methanol oxidation activity is low, the amount of the PtRu catalyst used is large, and generally about 3 to 10 mg / cm ^{2 is} used. When the amount of the PtRu catalyst is increased, the thickness of the catalyst layer is considerably increased, and in order to improve the diffusibility of methanol as a fuel, a PtRu black catalyst such as HiSPEC6000 manufactured by Johnson Matthey is generally used. However, since the particle size of the PtRu black catalyst is 5 nm or more, the methanol oxidation activity per catalyst mass is low, and the proportion of PtRu that does not contribute to the catalytic reaction is high. Therefore, it is preferable to use a catalyst in which small PtRu particles are supported on a conductive carbon support with good dispersibility. Furthermore, in order to make the layer thickness of the catalyst as thin as possible, it is desirable to increase the amount of PtRu particles supported on carbon as much as possible.

For example, as a means for obtaining a catalyst such as a highly supported and highly dispersed PtRu supported catalyst, an average particle diameter of 4 nm or less is obtained by forming a metal nucleus such as Pt on the carrier carbon and then growing PtRu or the like on the metal nucleus. It has been reported that it is possible to obtain a catalyst in which particles such as PtRu particles are supported on carbon even at a loading rate of 50% by mass or more (Patent Document 1: Japanese Patent Application Laid-Open No. 2007-134295). However, further improvement in methanol oxidation activity is desired for practical use.

For durability, see, for example, Piotr Piela et al. , Journal of Electrochemical Society, 151 (12), A2053-A2059, 2004 (Non-patent Document 1), during DMFC operation, Ru of the PtRu catalyst elutes and Ru crosses over to the cathode side. There is a problem that the Pt catalyst on the cathode side is poisoned and the oxygen reduction characteristics of the cathode deteriorate. Ru elution occurs due to potential fluctuations, and it is said that the alloying degree, crystallinity, and presence of Ru oxide species of PtRu affect the stability, but it is not known clearly. For example, Inaba et al., Fuel Cell, 6, 17-21, 2007 (Non-patent Document 2)).

JP 2007-134295 A

The present invention has been made in view of the above circumstances, and provides a fuel cell electrode catalyst that has high methanol oxidation activity and is stable against potential fluctuations, and that is particularly effective for direct methanol fuel cells, and a method for producing the same. With the goal.

As a result of intensive studies to achieve the above object, the inventor of the present invention has evaluated platinum in the atmosphere as an electrode catalyst for a fuel cell obtained by growing a catalytic metal containing platinum and ruthenium using metal fine particles as a nucleus. In the catalyst metal containing ruthenium, the average coordination number of the first adjacent platinum atom around the ruthenium atom is 3.5 or more, the change in the active surface area per mass of the metal fine particle with respect to the potential fluctuation is small, and the change in the methanol oxidation activity Was found to be smaller.

Such an electrode catalyst for a fuel cell is a method (2) in which a metal nucleus (single metal or alloy nucleus) is formed on the carrier carbon, and then a metal (metal simple substance or alloy) is further grown on the metal nucleus. In the stage loading method), after forming a metal nucleus on the support carbon, when growing a catalytic metal containing platinum and ruthenium such as PtRu, as a Ru raw material to be used, the following formula (A)
M ₂ RuX ₆ (A)
(Wherein M is one or more selected from H, Li, Na, K and NH ₄ , and X is one or more selected from Cl, Br, I and NO ₃ )
It is realized by reducing and growing a ruthenium compound in which the valence of Ru is tetravalent, particularly H ₂ RuCl ₆ , and a conventional two-stage loading method using a trivalent Ru raw material. Compared to those prepared in the above and commercially available PtRu black catalysts, the stability against potential fluctuation is improved, and the methanol oxidation activity per catalyst metal mass is improved especially at a potential of 0.4 to 0.6 V vs. RHE. The headline and the present invention have been made.

Accordingly, the present invention provides the following fuel cell electrode catalyst and method for producing the same.
[1] A fuel cell electrode catalyst obtained by growing a catalyst metal containing platinum and ruthenium using metal fine particles as a nucleus, and the first adjacent platinum around the ruthenium atom in the catalyst metal containing platinum and ruthenium in the atmosphere An electrode catalyst for fuel cells, wherein the average coordination number of atoms is 3.5 or more.
[2] A fuel cell electrode catalyst obtained by growing a catalyst metal containing platinum and ruthenium with metal fine particles as nuclei on a conductive carbon support, and ruthenium in the catalyst metal containing platinum and ruthenium in the atmosphere. An electrode catalyst for a fuel cell, wherein an average coordination number of first adjacent platinum atoms around the atom is 3.5 or more.
[3] A first supporting step for generating metal fine particles having a particle diameter of 0.1 to 2.0 nm with controlled particle spacing on a conductive carbon support, and a catalytic metal containing platinum and ruthenium with the metal fine particles as a nucleus, A method for producing an electrode catalyst for a fuel cell, comprising a second supporting step of growing a metal compound containing a platinum compound and a ruthenium compound by reducing with a reducing agent,
In the second supporting step, as the ruthenium compound, the following formula (A)
M ₂ RuX ₆ (A)
(Wherein M is one or more selected from H, Li, Na, K and NH ₄ , and X is one or more selected from Cl, Br, I and NO ₃ )
The method for producing a fuel cell electrode catalyst according to [2], wherein a ruthenium compound represented by the formula (2) is used.
[4] The method for producing an electrode catalyst for a fuel cell according to [3], wherein the ruthenium compound is H ₂ RuCl ₆ .

The electrode catalyst for a fuel cell of the present invention has an improved methanol oxidation activity per mass of the catalyst as compared to a commercially available PtRu black catalyst or a conventional PtRu-supported carbon catalyst prepared using a trivalent Ru raw material, and is due to potential fluctuations. It is a stable fuel cell electrode catalyst with small fluctuations in active surface area and methanol oxidation activity. By using this as an anode catalyst of a fuel cell, a high-performance fuel cell can be provided.

The fuel cell electrode catalyst of the present invention is obtained by growing a catalytic metal containing platinum and ruthenium using metal fine particles as nuclei. The average coordination number of the first adjacent platinum atoms around the ruthenium atom in the catalyst metal containing platinum and ruthenium in the atmosphere of the electrode catalyst is 3.5 or more, preferably 3.7 or more.

The average coordination number of the first adjacent platinum atoms around the ruthenium atom can be calculated by measuring EXAFS (Extended X-ray Absorption Fine Structure) at the Ru K absorption edge and analyzing it. EXAFS is a vibration structure that appears on the high energy side of the X-ray absorption spectrum, and this vibration structure is backscattered by the emitted waves of photoelectrons emitted from the X-ray absorption atoms and the atoms present around the absorption atoms. This is due to the interference effect with the incident wave of electrons. The amplitude is proportional to the number of atoms present around the absorbing atom, that is, the coordination number. Therefore, by analyzing the EXAFS spectrum of the Ru K absorption edge, it is possible to evaluate what kind of element is coordinated around the Ru atom.

The coordination of the first adjacent platinum atom around the ruthenium atom is in the range where the bond distance is the shortest from the absorbing Ru atom, and there are usually a plurality of coordination. In the PtRu fine particles, for example, the number of coordination (that is, the number of first adjacent platinum atoms) differs between the case where the absorbed Ru atoms are present inside the fine particles and the case where they are present on the surface of the fine particles. In the present invention, the average coordination number of the first adjacent platinum atoms around the ruthenium atom is the average coordination number of the first adjacent platinum atoms of a large number of ruthenium atoms present at various positions in the catalyst metal.

When the average coordination number of the first adjacent platinum atoms around the ruthenium atom in the catalyst metal containing platinum and ruthenium is in the above range, the change in the active surface area per mass of fine metal particles with respect to the potential fluctuation of the electrode catalyst is small, and methanol oxidation Small change in activity. Therefore, a high-performance fuel cell can be obtained by using such an electrode catalyst as an electrode catalyst (anode catalyst) for a fuel cell.

The fuel cell electrode catalyst of the present invention is particularly preferably one obtained by growing a catalytic metal containing platinum and ruthenium on a conductive carbon support with metal fine particles as a nucleus. Such an electrode catalyst for a fuel cell of the present invention is a method in which a metal nucleus (single metal or alloy nucleus) is formed on a carrier carbon, and then a metal (metal simple substance or alloy) is further grown on the metal nucleus ( It can be produced by a two-stage loading method).

The two-stage loading method, which is a method for producing this fuel cell electrode catalyst,
i. A first supporting step of generating fine metal particles having a particle size of 0.1 to 2.0 nm with a controlled particle spacing on a conductive carbon carrier;
ii. A method comprising a second supporting step of growing a catalytic metal containing platinum and ruthenium by reducing the metal compound containing platinum compound and ruthenium compound with a reducing agent using the metal fine particle as a nucleus can be applied.

Here, as the conductive carbon carrier used in the first supporting step, acetylene black, furnace black, channel black, activated carbon, graphite, carbon nanotube, carbon nanofiber, carbon nanocoil, mesoporous carbon and the like can be used. In this case, the average primary particle size of the conductive carbon support is preferably 10 to 200 nm, particularly 10 to 50 nm. If the average particle size is smaller than the above range, it may be difficult to uniformly disperse carbon and carry metal fine particles having an average particle size of 1.5 nm or less. If the average primary particle size is larger than the above range, the unit Since the amount of metal per volume is reduced, in order to place a predetermined amount of catalyst at the time of fuel cell production, the catalyst layer becomes thick and it may be difficult to supply fuel. In the present invention, the particle size such as the average primary particle size can be measured, for example, by observing a 2 million times image with a transmission electron micrograph, and the average value is, for example, about 300 particle sizes. Can be obtained as an average value when measured.

Further, as the metal supported on the carbon carrier, Pt, Au, Ag, Ir, Os, Pd, Rh, Ru, Cu, Ni, Co, Fe, Mn, Cr, V, Ti, Mo, W, Ta, Bi, Sn, etc. are mentioned. In particular, Pt or Ru is preferable because of the high active surface area when the same mass is supported. These metals are produced and supported as fine particles having an average particle size of 0.1 to 2.0 nm with controlled particle spacing on the carbon support. Here, “controlling the particle spacing” means that the fine particles are uniformly dispersed on the carbon surface without agglomerating, and the method for controlling the particle spacing is 30% by mass. The metal raw material is reduced at a loading rate of less than 30% by weight, preferably at a loading rate of 15% by mass or less, and the metal raw material is reduced in the presence of carbon in the liquid phase. A method such as impregnation with carbon and reduction in the gas phase, or loading a metal colloid on carbon with a loading rate of less than 30% by mass, preferably a loading rate of 15% by mass or less can be employed.

Further, as described above, the nucleation by the metal fine particles in the first supporting step is set to a particle size of 2.0 nm or less, preferably 1.5 mm or less. When it is larger than 2.0 nm, the particle diameter of the finally obtained catalyst particles is large and easily aggregated, so that a highly dispersed catalyst cannot be obtained. Moreover, when it forms in 2.0 nm or less, the coupling | bonding with a support | carrier is strong and it is easy to disperse | distribute uniformly on carbon.

As the method for generating and supporting the metal fine particles in the first supporting step, particularly when the fine platinum particles are generated and supported in the presence of carbon in the liquid phase, the carbon carrier is 0.01 to 2% by mass, particularly 0.1 to In an aqueous dispersion dispersed in water at a ratio of 1% by mass, chloroplatinate, platinum (II) chloride, platinum (IV) chloride, dinitrodiamine platinum (II), bisacetylacetonatoplatinum, dichlorotetramineplatinum, A platinum compound such as tetramine platinum sulfate, platinum (II) ammonium chloride, platinum (IV) ammonium chloride, dichlorodiamine platinum and a reducing agent such as ethylene glycol, ethanol, methanol, 1-propanol, 2-propanol, and butanol are added. In this case, the amount of the platinum compound is preferably 0.1 to 30% by mass, particularly 1 to 15% by mass with respect to the carbon support as platinum metal. If the amount of the platinum compound is too small, the number of growth nuclei on the carbon surface decreases, and if the amount of the platinum compound is too large, coarse particles are generated, and a catalyst with high loading and good dispersibility may not be obtained. The amount of the reducing agent such as ethylene glycol used is preferably 1 to 80% by mass, particularly 5 to 50% by mass in the aqueous dispersion. The pH of the aqueous dispersion is preferably 4 to 12, particularly 5 to 10. For this reason, sodium hydroxide, aqueous ammonia, tetrahydroxymethylammonium or the like is used as a pH adjuster, and the pH is within the above range. It is preferable to adjust. In addition, although the case where platinum fine particles were produced | generated was illustrated here, when producing | generating the metals mentioned above other than platinum, it can produce by changing a metal compound and a reducing agent suitably.

Subsequently, the mixed solution thus obtained is preferably stirred at 40 to 120 ° C., particularly 50 to 100 ° C., preferably for 1 to 10 hours, particularly 2 to 6 hours, and after filtration and washing, preferably 40 Carbon carrying metal fine particles can be obtained by drying at 150 to 150 ° C., particularly 60 to 120 ° C., preferably 3 to 24 hours, particularly 8 to 16 hours.

Here, the loading ratio of the metal fine particles after reduction is preferably 1 to 30% by mass, particularly 5 to 15% by mass. If the loading rate is too low, the number of growth nuclei on the carbon surface is not sufficient, and if the loading rate is too high, the size of the metal fine particles increases, and a catalyst with high loading rate and good dispersibility cannot be obtained. Here, the carrying rate is a value obtained from the following formula (1).
Loading ratio (mass%) = [A / (A + C)] × 100 (1)
A: Metal fine particle mass C: Carbon carrier mass

Next, after the metal fine particles are supported on the carbon support as described above, the same or other metal (catalyst metal) is grown using the metal fine particles as nuclei. In this case, the catalyst metal is a catalyst metal containing Pt and Ru, and as an alloy containing PtRu, in addition to the binary system of PtRu, PtRuSn, PtRuRh, PtRuPd, PtRuIr, PtRuAu, PtRuMo, PtRuW, PtRuCo, PtRuCo, PtRuCo Although ternary systems such as PtRuFe and PtRuCr are listed, PtRu is preferable in terms of high methanol oxidation activity.

It is possible to obtain a highly supported and highly dispersed catalyst by supporting or growing a catalyst metal such as PtRu on the metal fine particle nucleus such as Pt produced in the first stage, but it is finally formed. The average particle diameter of the catalyst metal such as PtRu is 4 nm or less, preferably 3 nm or less, more preferably 2.5 nm or less. In addition, although a minimum is not limited, Usually, it is 0.1 nm or more. If it is larger than 4 nm, the particle size becomes the same level as or larger than that of a commercially available PtRu black catalyst, and the methanol oxidation activity per metal mass may decrease.

The supporting rate of all metal particles after the second supporting step is 50% by mass or more, preferably 60% by mass or more. When the loading ratio is lower than 50% by mass, the dispersion of the fine catalyst metal particles is easy, but the catalyst layer at the time of manufacturing the membrane electrode assembly (MEA) becomes thicker than when a catalyst with a high loading ratio is used. For this reason, the supply of methanol fuel becomes rate limiting, and the output may be smaller than when a catalyst with a high loading rate is used. The upper limit of the loading rate is not particularly limited, but is usually 90% by mass or less, particularly preferably 75% by mass or less. In addition, the supporting rate here is calculated | required from following formula (2).
Loading ratio (mass%) = [(A + B) / (A + B + C)] × 100 (2)
A: Mass of metal core B: Mass of catalyst metal (for example, PtRu) C: Mass of carbon support

Here, as a method for growing a metal catalyst on the metal fine particle nucleus, for example, when growing PtRu, chloroplatinic acid, platinum (II) chloride, platinum (IV) chloride, dinitrodiamine platinum ( II), platinum compounds such as bisacetylacetonatoplatinum, dichlorotetramineplatinum, platinum tetraminesulfate, platinum (II) ammonium chloride, platinum (IV) ammonium chloride, dichlorodiamineplatinum and the like can be used alone or in combination.

On the other hand, as a ruthenium raw material, in the present invention, the following formula (A)
M ₂ RuX ₆ (A)
(Wherein M is one or more selected from H, Li, Na, K and NH ₄ , and X is one or more selected from Cl, Br, I and NO ₃ )
It is preferable to use a ruthenium compound in which the valence of ruthenium represented by is tetravalent.

Specific examples of the ruthenium compound include ruthenium chloride having a valence of 4 ruthenium chloride (H ₂ RuCl ₆ ), lithium ruthenate (Li ₂ RuCl ₆ ), sodium ruthenate (Na ₂ RuCl ₆ ), Ruthenium compounds such as ruthenium chlorate such as potassium ruthenate (K ₂ RuCl ₆ ) and ammonium ruthenate ((NH ₄ ) ₂ RuCl ₆ ) or salts thereof may be used alone or in combination. H ₂ RuCl ₆ is preferably used because of the high methanol oxidation activity of the finally obtained catalyst.

These platinum and ruthenium compounds are dissolved in a solution containing a reducing agent such as ethanol, methanol, 1-propanol, 2-propanol, butanol, ethylene glycol, and then a carbon carrier carrying metal fine particle nuclei is charged. A method is employed in which PtRu is produced and grown on the metal fine particle nuclei by reacting at 1 ° C., particularly 50 to 100 ° C. for 1 to 10 hours, particularly 2 to 8 hours. On the other hand, the concentration of platinum and ruthenium compounds in the solution is preferably 0.01 to 10% by mass, particularly 0.1 to 5% by mass in terms of catalyst metal. The concentration of the reducing agent is preferably 1 to 80% by mass, particularly 5 to 60% by mass.

The platinum compound and ruthenium compound are preferably used in a molar ratio of 2: 8 to 9: 1, particularly 5: 5 to 8: 2, as platinum metal: ruthenium metal. If the amount of the platinum compound is too small, the CH dissociation reaction of methanol does not proceed, so that the methanol oxidation current value becomes small. If it is too large, the oxidation reaction of methanol, which is a reaction intermediate product of methanol, hardly occurs, and the potential is low. Methanol oxidation activity at a potential of 0.4 V (vs RHE) or less is reduced. If the amount of the ruthenium compound is too small, the methanol oxidation activity at a low potential is low as in the case where the amount of platinum is large, and if it is too large, the methanol oxidation current value is small as in the case where the amount of platinum is small.

The amount of the carbon support carrying the metal fine particle nuclei is preferably 0.01 to 2% by mass, particularly 0.1 to 1% by mass dispersed in the solution. If the amount is too small, the amount of the resulting catalyst will be small, and if it is too large, the dispersibility of carbon will be poor, and metal particles will agglomerate and coarse particles will be produced. In addition, although the case where PtRu was grown was illustrated here, when producing | generating the metals mentioned above other than PtRu, it can produce | generate by changing a metal compound suitably.

The fuel cell electrode catalyst thus obtained is particularly preferably used as an anode electrode catalyst of a direct methanol fuel cell.

Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
Chloroplatinic acid containing 0.1 g of platinum is added to 500 ml of an aqueous dispersion containing 1 g of carbon support (Ketjen Black EC300J (manufactured by Lion Corporation)), and 500 g of ethylene glycol and 50 mmol of NaOH are added. did. This mixed solution was heated and stirred at 80 ° C. for 16 hours. After filtration and washing, it was dried at 80 ° C. for 16 hours to obtain carbon carrying Pt nuclei. As a result of TEM observation of the obtained carbon carrying Pt nuclei, it was confirmed that fine particles having a particle diameter of about 0.5 nm were uniformly dispersed on the carrier.

0.5 g of carbon carrying the Pt nucleus was added to 600 g of a solution containing 1.1 g of dinitrodiamineplatinum (II), 0.5 g of ruthenic acid chloride (H ₂ RuCl ₆ ) and 100 g of 2-propanol, The mixture was refluxed at 60 ° C. for 8 hours to obtain 1.4 g of a catalyst having a PtRu loading rate of 68% by mass. As a result of TEM observation, the average particle diameter was 2.4 nm, and it was uniformly dispersed on the carbon.

The active surface area was evaluated by the CO stripping method. The catalyst was ultrasonically dispersed in water and then dropped on a glassy carbon electrode. After drying, a 5% Nafion solution (manufactured by DuPont) was dropped to prepare an electrode for evaluation. The electrode was attached to a potentiostat (HZ5000 manufactured by Hokuto Denko) and immersed in an electrolytic cell containing 0.5 mol / L H ₂ SO ₄ . After replacing the atmosphere of the electrolysis cell with Ar, the catalyst was held at −0.18 V (vs RHE), and CO adsorption was performed by bubbling CO gas for 20 min. While maintaining the same potential, bubbling was performed with Ar gas for 20 min, and excess CO gas was discharged. After that, the potential was scanned at a sweep range of -0.18 to 0.5 V (vs RHE), a sweep speed of 10 mV / s, the CO stripping voltamgram was measured, and the potential was scanned again after CO was desorbed. The active surface area of PtRu was calculated on the assumption that the difference was the CO oxidation current and the Coulomb charge of CO oxidation was 4.2 C / m ² .

Methanol oxidation activity was evaluated by setting the electrolyte to 0.5 mol / L H ₂ SO ₄ +1 mol / L CH ₃ OH, the oxidation range at a sweep range of −0.18 to 0.5 V (vs RHE), and a sweep rate of 1 mV / s. Evaluated. The active area evaluation and methanol oxidation activity were all performed at 25 ° C.

Evaluation of stability against potential fluctuation is performed according to Yoshioka et al., NEDO Symposium “Prospects for high durability of polymer electrolyte fuel cells”, 30-36, 2007 (Non-patent Document 3). Performed according to the method. After evaluating the methanol oxidation activity, the electrolyte was changed to 0.5 mol / L H ₂ SO ₄ and a load fluctuation simulation test of 2400 cycles was performed at 0.05 to 0.4 V (vs RHE) and a sweep rate of 100 mV / s. After the potential cycle, the active surface area and methanol oxidation activity were evaluated in the same procedure as described above. Stability was confirmed from changes in the active surface area and methanol oxidation activity before and after this load fluctuation cycle.

The average coordination number of the first adjacent platinum atom around the ruthenium atom was calculated by measuring EXAFS (Extended X-ray Absorption Fine Structure) at the Ru K absorption edge and analyzing it.

EXAFS measurements were performed at the Research Center for High-Intensity Photoscience and the Large Synchrotron Radiation Facility Spring-8 BL14B2. Si (111) was used as the spectral crystal, and the absorption spectrum was measured in the range of −200 eV to +1500 eV with respect to the K absorption edge 22117 eV of Ru. A sample was formed by using a BN powder as a binder, and after forming into a pellet form, placing it in a beam and performing a transmission method. The measurement atmosphere is air and the temperature is room temperature.

For analysis of the measured X-ray absorption spectrum, an IFEFFIT program package (for example, M. Newville, Journal of Synchrotron Radiation, 8, 314-316, 2001 (Non-Patent Document 4), JJ Rehr et al., Review) of Modern Physics, 72, 621-654, 2000 (see Non-Patent Document 5)).

[Example 2]
0.5 g of carbon carrying Pt nuclei prepared in the same procedure as in Example 1, 1.1 g of dinitrodiamine platinum (II), 0.7 g of potassium ruthenate (K ₂ RuCl ₆ ), and 100 g of 2-propanol The solution was charged into 600 g of the solution and refluxed at 80 ° C. for 8 hours to obtain 1.4 g of a catalyst having a PtRu loading rate of 68 mass%. As a result of TEM observation, the average particle diameter was 2.4 nm, and it was uniformly dispersed on the carbon. In the same manner as in Example 1, after evaluating the active surface area and methanol oxidation activity, a load fluctuation cycle was performed to evaluate the active surface area and methanol oxidation activity.

[Comparative Example 1]
0.5 g of carbon carrying Pt nuclei prepared in the same procedure as in Example 1, 1.1 g of dinitrodiamine platinum (II), and 0.5 g of ruthenium chloride (RuCl ₃ ) having a trivalent valence as a ruthenium raw material The solution was put into 600 g of a solution containing 100 g of 2-propanol and refluxed at 80 ° C. for 8 hours to obtain 1.4 g of a catalyst having a PtRu loading rate of 68 mass%. As a result of TEM observation, the average particle diameter was 2.2 nm, and it was uniformly dispersed on the carbon. In the same manner as in Example 1, after evaluating the active surface area and methanol oxidation activity, a load fluctuation cycle was performed to evaluate the active surface area and methanol oxidation activity.

[Comparative Example 2]
About the commercial catalyst PtRu black HiSPEC6000 (manufactured by Johnson Matthey), the active surface area and methanol oxidation activity were evaluated before and after the load fluctuation cycle in the same manner as in Example 1.

Table 1 shows the evaluation results of active surface area and 0.4 V, 0.5 V (vs RHE) methanol oxidation activity before and after the load fluctuation cycle for the catalysts of Examples 1 and 2 and Comparative Examples 1 and 2.

In addition, Table 2 shows the element types and the average coordination number of the Ru atom first adjacent element calculated by analyzing the EXAFS spectrum of the Ru K absorption edge.

In Table 1, when comparing the methanol oxidation activity before the load fluctuation cycle of Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that the catalysts obtained in Examples 1 and 2 have high methanol oxidation activity. . Regarding the stability, when comparing the active surface area before and after the load fluctuation cycle, the catalyst shown in the comparative example has a high reduction rate of the active area after the cycle, whereas the catalyst shown in the example shows the reduction rate. Is low. When comparing the methanol oxidation activity before and after the load fluctuation, it can be seen that the catalyst shown in the example hardly changes, whereas the catalyst shown in Comparative Example 1 has a markedly reduced methanol oxidation activity. From the above, a catalyst prepared using a tetravalent Ru compound as a raw material has high methanol oxidation activity and stability against potential fluctuation is also improved compared to a catalyst prepared using a trivalent Ru compound and HiSPEC6000. You can see that In particular, a catalyst using H ₂ RuCl ₆ as a raw material has improved methanol oxidation activity and potential stability.

In Table 2, when the element species coordinated to Ru and the coordination number thereof are compared, there is no difference in the coordination numbers of oxygen and Ru in Examples 1, 2 and Comparative Example 2. Comparing the coordination number of Pt atoms coordinated to Ru, it can be seen that the catalysts of Examples 1 and 2 are higher than the catalysts of Comparative Examples 1 and 2. The active area reduction rate after the load fluctuation cycle shown in Table 1 and the first neighboring Pt coordination number of Ru correspond well, and have a stability exceeding HiSPEC 6000 when the coordination number is 3.5 or more. I understand that. From the above, in the case of Ru having a first adjacent Pt coordination number of 3.5 or more, a catalyst prepared using a trivalent Ru salt, methanol oxidation activity exceeding HiSPEC 6000, and stability against potential fluctuation can be obtained. I understand.

Claims

An electrode catalyst for a fuel cell formed by growing a catalyst metal containing platinum and ruthenium using metal fine particles as a nucleus, and the average of the first adjacent platinum atoms around the ruthenium atom in the catalyst metal containing platinum and ruthenium in the atmosphere A fuel cell electrode catalyst having a coordination number of 3.5 or more.
An electrode catalyst for a fuel cell in which a catalyst metal containing platinum and ruthenium is grown on a conductive carbon support using metal fine particles as a nucleus, and around the ruthenium atoms in the catalyst metal containing platinum and ruthenium in the atmosphere. An electrode catalyst for a fuel cell, wherein the average coordination number of first adjacent platinum atoms is 3.5 or more.
A first supporting step for generating metal fine particles having a particle size of 0.1 to 2.0 nm with a controlled particle interval on a conductive carbon support; and a catalyst metal containing platinum and ruthenium using the metal fine particles as a nucleus, a platinum compound and A method for producing a fuel cell electrode catalyst comprising a second supporting step of growing a metal compound containing a ruthenium compound by reducing with a reducing agent,
In the second supporting step, as the ruthenium compound, the following formula (A)
M 2 RuX 6 (A)
(Wherein M is one or more selected from H, Li, Na, K and NH 4 , and X is one or more selected from Cl, Br, I and NO 3 )
A method for producing a fuel cell electrode catalyst according to claim 2, wherein the ruthenium compound represented by the formula (1) is used.
The ruthenium compound, H 2 RuCl 6 a process according to claim 3, wherein the fuel cell electrode catalyst, characterized in that.