JP2011150867A - Manufacturing method of ternary system electrode catalyst for fuel cell, and solid polymer fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To aim at reduction of a use volume of expensive platinum, by providing a manufacturing method of electrode catalyst for a fuel cell of high four-electron reduction performance and high activity. <P>SOLUTION: In the manufacturing method of ternary system electrode catalyst for the fuel cell with catalyst components consisting of platinum, cobalt, and at least another kind of metal M with a melting point lower than that of cobalt carried on a carbon carrier, a composition (atomic ratio) of platinum:cobalt:the metal M in the catalyst components is to be 1:0.11 to 0.19:0.02 to 0.11. The platinum, the cobalt and the metal M are to be alloyed at a temperature higher than the melting point of the metal M and lower than the melting point of cobalt. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a ternary electrode catalyst for a fuel cell that improves the performance of a platinum alloy catalyst, and a polymer electrolyte fuel cell using the same.

  A gas diffusible electrode used in a polymer electrolyte fuel cell includes a catalyst layer containing catalyst-supported carbon coated with an ion exchange resin, and a gas that supplies a reaction gas to the catalyst layer and collects electrons. It consists of a diffusion layer. In the catalyst layer, there are voids composed of fine pores formed between carbon secondary particles or tertiary particles as a constituent material, and the voids function as a diffusion flow path for the reaction gas. is doing.

  Conventionally, as a cathode and an anode catalyst of an electrode catalyst of a polymer electrolyte fuel cell, a catalyst in which a noble metal such as platinum or a platinum alloy is supported on carbon black has been used. Platinum-supported carbon black is obtained by adding sodium hydrogen sulfite to a chloroplatinic acid aqueous solution, then reacting with hydrogen peroxide solution, supporting the resulting platinum colloid on carbon black, washing, and heat-treating as necessary. It is common to prepare. The electrode of a polymer electrolyte fuel cell is prepared by dispersing platinum-supported carbon black in a polymer electrolyte solution, preparing an ink, applying the ink to a gas diffusion substrate such as carbon paper, and drying. . An electrolyte membrane-electrode assembly (MEA) is assembled by sandwiching a polymer electrolyte membrane between these two electrodes and performing hot pressing.

  Platinum is an expensive noble metal and it is desired to exhibit sufficient performance with a small amount of support. Therefore, studies have been made to increase the catalytic activity with a smaller amount. For example, Patent Document 1 below provides a fuel cell electrode catalyst that suppresses the growth of platinum particles during operation and has high durability performance. As an object, there is disclosed an electrocatalyst composed of a conductive carbon material, metal particles supported on the conductive carbon material that are less likely to be oxidized than platinum under acidic conditions, and platinum covering the outer surface of the metal particles. Specifically, examples of the metal particles include an alloy made of platinum and at least one metal selected from gold, chromium, iron, nickel, cobalt, titanium, vanadium, copper, and manganese.

  In addition, Patent Document 2 listed below has a predetermined amount in addition to a metal catalyst selected from the group consisting of platinum and a platinum alloy in the cathode catalyst layer for the purpose of obtaining excellent battery polarization characteristics and high battery output. Incorporation of a metal complex having iron or chromium is described, thereby improving the polarization characteristics of the cathode. Specifically, a solid polymer fuel cell comprising an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, the cathode comprising a gas diffusion layer and the gas diffusion layer A catalyst layer disposed between the layer and the polymer electrolyte membrane, wherein the catalyst layer contains a noble metal catalyst selected from the group consisting of platinum and a platinum alloy, and a metal complex containing iron or chromium. In addition, the metal complex is contained in an amount of 1 to 40 mol% of the total amount of the metal complex and the noble metal catalyst.

  Furthermore, in Patent Document 3 below, a platinum-gold alloy is deposited on a carbon support, and then an organic acid amine of two or more metals selected from nickel, cobalt and manganese is added and heated at a low temperature, A platinum alloy catalyst obtained by alloying a platinum-gold alloy with two or more metals selected from nickel, cobalt and manganese is disclosed. In addition, the catalyst component specifically disclosed in Patent Document 3 is platinum: cobalt: gold: manganese = 40 to 90: 4 to 28: 1 to 8: 4 to 28.

Japanese Patent Laid-Open No. 2002-289208 JP 2002-15744 A JP-A-4-141236

  The catalysts described in Patent Documents 1 and 2 have insufficient four-electron reduction performance, and the development of higher performance catalysts has been desired.

  Cobalt has good electrical characteristics and has been conventionally used as an alloy catalyst. However, since the melting point of cobalt is high, a large amount of energy is required for alloying with platinum, and since it has a high melting point, it is difficult to mix with platinum. In addition, when applying a large amount of energy, if the solid solution is formed at a high temperature, the particle size of the catalyst metal becomes large, so that the power generation performance decreases. Therefore, in the method for producing a platinum alloy catalyst described in Patent Document 3, a large amount of energy is required, alloying is not sufficient, and catalytic activity is not high.

  The present invention achieves alloying of a ternary electrode catalyst for a fuel cell in which a catalyst component composed of platinum, cobalt, and a third metal M is supported on a carbon support with a small amount of energy. It aims at providing the manufacturing method which makes the catalyst for high performance high performance.

  The present inventors have found that the above problem can be solved by selecting a specific third metal M and alloying at a specific temperature, and have reached the present invention.

  That is, first, the present invention relates to a method for producing a ternary electrode catalyst for a fuel cell in which a catalyst component comprising platinum, cobalt, and at least one metal M having a melting point lower than cobalt is supported on a carbon support. The composition (atomic ratio) of platinum: cobalt: metal M in the catalyst component is 1: 0.11-0.19: 0.02-0.11, and these platinum, cobalt, and metal M are And alloying at a temperature higher than the melting point of the metal M and lower than the melting point of cobalt.

  The ternary electrode catalyst for fuel cells produced according to the present invention is sufficiently alloyed and has excellent power generation performance because the particle size of the catalyst component is not enlarged. That is, by using a metal M having a melting point lower than that of cobalt and processing at a temperature higher than the melting point of the metal M and lower than the melting point of cobalt, the liquefied metal M solidifies the cobalt and further solidifies the platinum. Thus, a ternary alloy can be obtained, and a ternary catalyst can be produced with low energy (low temperature). As a result, the particle size of the catalyst component is prevented from increasing, and the power generation performance is improved.

  Further, when the molar ratio of cobalt to metal M is 1: 9.5 to 1: 1, a ternary electrode catalyst with improved power generation characteristics is obtained, and the amount of platinum used can be reduced. When the molar ratio of cobalt to metal M is less than 1: 9.5 (= when the amount of cobalt is small), the metal that contributes to the activity decreases, so the electrical characteristics deteriorate. When the molar ratio of cobalt to metal M is greater than 1: 1 (= when the amount of cobalt is large), since the amount of metal M that can solidify cobalt is small, all of cobalt cannot be solidified, Cannot solidify all platinum, so that the effect as a three-way catalyst cannot be obtained.

  The metal M, which is one of the catalyst components of the ternary electrode catalyst produced in the present invention, is selected from metals having a melting point lower than that of cobalt. Since the melting point of cobalt is 1495 ° C., manganese (melting point: 1246 ° C.), copper (melting point: 1084.4 ° C.), gold (melting point: 1064.2 ° C.), silver (melting point: 961 ° C.), nickel (melting point) : 1455 ° C.) and zinc (melting point: 419.5 ° C.). In addition, although this invention concerns on the manufacturing method of the ternary system electrode catalyst for fuel cells, you may use 1 or more types of the metal M. FIG.

  In the present invention, when the metal M is used, the alloying temperature is preferably 962-1495 ° C. as a specific range.

  Secondly, the present invention relates to a polymer electrolyte fuel cell comprising a fuel cell electrode catalyst produced by the above method.

  The electrode catalyst for fuel cells of the present invention has high four-electron reduction performance and high activity as compared with conventional platinum alloy catalysts.

The melting points of metals other than Pt and Co used in Examples and Comparative Examples are shown. The metal species and initial performance results are shown. The relationship between the ratio of Co: Mn and catalyst performance is shown.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[Example: Preparation of Pt-Co-Mn / C catalyst]
A Pt—Co—Mn / C catalyst was prepared by the following procedure.
[Example 1]
Commercially available KetjenEC (made by Ketjen Black International) 5.0 g of hexahydroxo platinum nitric acid solution containing 4.54 g of platinum and pure water so that Co nitrate has a Co content of 0.4 g and Mn nitrate has a Mn content of 0.08 g. Added to 0.5 L and dispersed. About 100 mL of 0.1N ammonia was added thereto to adjust the pH to about 10, and a hydroxide was formed and precipitated on carbon.

  The dispersion was filtered, and the resulting powder was vacuum-dried at 100 ° C. for 10 hours. Next, after reducing in hydrogen gas at 400 ° C. for 2 hours, reduction treatment was performed in nitrogen gas at 1000 ° C. for 10 hours to obtain an alloy powder.

  Pt was not detected from the waste liquid analysis of the obtained catalyst powder, and it was confirmed that all Pt was supported. The catalyst powder was stirred with 1.0N nitric acid. Stirring was performed at room temperature for 2 hours. The stirred solution was filtered, and from the waste liquid analysis of the filtrate (quantitative determination of Pt, Co, Mn), Pt: 45.40 wt%, Co: 1.57 wt%, Mn: 1.43 wt%, C: 51.00 wt% Met. Here, the molar ratio of cobalt and manganese was 1.0: 1.0. Further, the particle diameter of the catalyst was 5.0 nm as calculated from the peak position of the XRD Pt (111) plane (Scherrer equation). The solid solution of the additive element was confirmed from the composition of the particles by EDX analysis.

[Example 2]
The amount of Mn nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production of Example 1. The obtained catalyst composition was Pt: 45.50 wt%, Co: 1.75 wt%, Mn: 1.25 wt%, C: 51.50 wt%. Here, when the molar ratio of cobalt and manganese was compared, it was 1.3: 1.0.

[Example 3]
The amount of Mn nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production of Example 1. The obtained catalyst composition was Pt: 46.50 wt%, Co: 2.6 wt%, Mn: 0.4 wt%, C: 50.50 wt%. Here, when the molar ratio of cobalt and manganese was compared, it was 6.1: 1.0.

[Example 4]
The amount of Mn nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production of Example 1. The obtained catalyst composition was Pt: 46.70 wt%, Co: 2,72 wt%, Mn: 0.28 wt%, C: 50.30 wt%. Here, when the molar ratio of cobalt and manganese was compared, it was 9.1: 1.0.

[Comparative Example 1]
The amount of Co nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production in Example 1. The obtained catalyst composition was Pt: 46.50 wt%, Co: 0.3 wt%, Mn: 2.7 wt%, and C: 50.50 wt%. Here, the molar ratio of cobalt and manganese was 0.1: 1.0.

[Comparative Example 2]
The amount of Co nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production in Example 1. The obtained catalyst composition was Pt: 46.00 wt%, Co: 1.35 wt%, Mn: 1.65 wt%, C: 51.00 wt%. Here, when the molar ratio of cobalt and manganese was compared, it was 0.8: 1.0.

[Comparative Example 3]
The amount of Mn nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production of Example 1. The obtained catalyst composition was Pt: 47.00 wt%, Co: 2.75 wt%, Mn: 0.25 wt%, and C: 50.00 wt%. Here, when comparing the molar ratio of cobalt and manganese, it was 10.3: 1.0.

[Comparative Example 4]
The amount of Mn nitrate added was reduced, and a catalyst was produced in the same manner as the catalyst production of Example 1. The obtained catalyst composition was Pt: 45.40 wt%, Co: 2.78 wt%, Mn: 0.22 wt%, C: 51.60 wt%. Here, when the molar ratio of cobalt and manganese was compared, it was 11.8: 1.0.

[Example 5]
A catalyst was prepared in the same manner as in Example 1 except that Mn nitrate was Au chloride. The obtained catalyst composition was Pt: 45.80 wt%, Co: 1.84 wt%, Au: 1.16 wt%, and C: 51.20 wt%. Here, when the molar ratio of cobalt and gold was compared, it was 5.3: 1.0.

[Example 6]
A catalyst was prepared in the same manner as the catalyst preparation in Example 1, except that Mn nitrate was Cu sulfate. The obtained catalyst composition was Pt: 45.40 wt%, Co: 2.48 wt%, Cu: 0.52 wt%, C: 51.60 wt%. Here, when comparing the molar ratio of cobalt and copper, 5.1. : 1.0.

[Example 7]
A catalyst was prepared in the same manner as in Example 1 except that Mn nitrate was Ag nitrate. The obtained catalyst composition was Pt: 45.90 wt%, Co: 2.24 wt%, Ag: 0.76 wt%, and C: 51.10 wt%. Here, when the molar ratio of cobalt and silver was compared, it was 5.4: 1.0.

[Comparative Example 5]
A catalyst was prepared in the same manner as in the preparation of the catalyst of Example 1 using Mn nitrate as Fe nitrate. The obtained catalyst composition was Pt: 47.00 wt%, Co: 2.53 wt%, Fe: 0.47 wt%, and C: 50.00 wt%. Here, when the molar ratio of cobalt and iron was compared, it was 5.1: 1.0.

[Comparative Example 6]
A catalyst was prepared in the same manner as the catalyst preparation in Example 1, except that Mn nitrate was Cr nitrate. The obtained catalyst composition was Pt: 46.30 wt%, Co: 2.56 wt%, Cr: 0.44 wt%, C: 50.70 wt%. Here, when the molar ratio of cobalt and chromium was compared, it was 5.1: 1.0.

[Comparative Example 7]
A catalyst was prepared in the same manner as in Example 1 except that Mn nitrate was Rh nitrate. The catalyst composition was Pt: 47.30 wt%, Co: 2.22 wt%, Rh: 0.78 wt%, C: 49.30 wt%. Here, the molar ratio of cobalt and rhodium was 5.3: 1.0.

[Initial performance measurement]
In order to compare the catalyst performance in the initial stage, the initial voltage measurement was performed as follows. The cell temperature of the single cell was set to 80 ° C., the humidified air that passed the humidified bubbler through the cathode side electrode was RH100, the stoichiometric ratio was 7.5, and the humidified hydrogen that was passed through the humidified bubbler through the anode side electrode was RH100, The stoichiometric ratio was 7.5 and the current-voltage characteristics were measured using an electronic load. The Pt amount of each electrode was 0.3 mg / cm ² .

  Table 1 summarizes the catalyst composition, numerical processing results, and battery performance for Examples 1 to 7 and Comparative Examples 1 to 7.

  FIG. 1 shows melting points of metals other than Pt and Co used in Examples and Comparative Examples. The problem of ternary alloying is that the three elements are completely dissolved. The present invention is characterized in that the third element is alloyed with a highly active species of Pt and Co. Here, by selecting a metal having a melting point lower than that of Co as the third metal M, it is possible to obtain a highly active catalyst having a low melting point and solid solution of three elements.

  Next, the evaluation results of the catalyst in which the third element is alloyed with the highly active species of Pt and Co are shown. From Table 1, Examples 3, 4, 5, 6 and Comparative Examples 5, 6, 7 were selected from Table 1. FIG. 2 shows the results of the metal species and initial performance. The evaluation between samples was made with the aim of Co: metal M = 5: 1. Measurements were made in a range where there was no difference in performance due to the difference in ratio.

  2 shows that a metal having a lower melting point than that of Co shown in FIG. 1 is a highly active catalyst. This is presumably due to the alloying effect of the ternary alloy.

  In Table 2, the performance of the catalyst in which Pt, Co, and Mn were fixed and the ratio of Co: Mn was changed was examined. FIG. 3 shows the relationship between the Co: Mn ratio and the catalyst performance.

  It can be seen from Table 2 and FIG. 3 that high performance can be obtained specifically in the range of Co: Mn ratio of 1: 1 to 9.5: 1.

  The fuel cell electrode catalyst of the present invention has high four-electron reduction performance and high activity, and is useful for reducing the amount of expensive platinum used. This contributes to the practical application and spread of fuel cells.

Claims (4)

  A method for producing a ternary electrode catalyst for a fuel cell in which a catalyst component comprising platinum, cobalt, and at least one metal M having a melting point lower than cobalt is supported on a carbon carrier, wherein platinum: cobalt in the catalyst component : The composition (atomic ratio) of the metal M is 1: 0.11 to 0.19: 0.02 to 0.11, and these platinum, cobalt, and metal M are higher than the melting point of the metal M and lower than the melting point of cobalt. A method for producing a ternary electrode catalyst for a fuel cell, characterized by being alloyed with   The method for producing a ternary electrode catalyst for a fuel cell according to claim 1, wherein the metal M is one or more selected from manganese, copper, gold, silver, nickel, and zinc.   The method for producing a ternary electrode catalyst for a fuel cell according to claim 1 or 2, wherein the alloying temperature is 962 to 1495 ° C. The polymer electrolyte fuel cell provided with the electrode catalyst for fuel cells obtained by the manufacturing method of any one of Claims 1-3.

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