JP2010003576A - Electrode catalyst for fuel cell, its manufacturing method, and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a highly active electrode catalyst for a fuel cell replacing platinum and having high four-electron reduction performance and a high recycling property without using Fe carbonyl or Ni carbonyl which is a toxic substance in a manufacturing process. <P>SOLUTION: The method of manufacturing the electrode catalyst for the fuel cell represented by M<SB>1</SB>M<SB>2</SB>X (M<SB>1</SB>is Ru, M<SB>2</SB>is Fe and/or Ni, and X is at least one kind of chalcogen element) has processes for mixing alcohol and water with at least one kind of compound selected from an Fe nitric acid compound, an Ni nitric acid compound, an Fe hydrochloric acid compound and an Ni hydrochloric acid compound; adding an Ru chalcogen compound while agitating a mixture; adding a reducing agent while agitating the mixture to reduce the Fe and/or Ni compound; filtering and washing a product; and heat-treating the filtered object. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a novel fuel cell electrode catalyst excellent in initial activity and durability, which is an alternative to a conventional platinum catalyst, a production method thereof that does not use harmful substances such as Fe carbonyl, Ni carbonyl, and fuel using the same It relates to batteries.

  Platinum or a platinum alloy-based catalyst is mainly used as the anode catalyst for the polymer electrolyte fuel cell. Specifically, a catalyst in which a noble metal including platinum 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, reacting with hydrogen peroxide solution, adsorbing the resulting platinum colloid to carbon black, washing, and heat-treating as necessary. The preparation method is general. In a polymer electrolyte fuel cell, platinum-supported carbon black is dispersed in a polymer electrolyte solution to form a paste. The paste is applied to a gas diffusion electrode such as carbon paper, dried, and then dried with two gas diffusion electrodes. An electrolyte membrane-electrode assembly (MEA) is manufactured by sandwiching a molecular electrolyte membrane and performing hot pressing.

  One of the problems in putting a polymer electrolyte fuel cell into practical use is material cost. One means for solving this is to reduce the amount of platinum.

On the other hand, it is known that when oxygen (O ₂ ) is electrolytically reduced, superoxide is generated by one-electron reduction, hydrogen peroxide is generated by two-electron reduction, and water is generated by four-electron reduction. In a fuel cell stack using platinum or a platinum-based catalyst as an electrode, if a voltage drop occurs for some reason, the 4-electron reducibility is reduced and the 2-electron reducibility is obtained. For this reason, hydrogen peroxide is generated, which causes deterioration of MEA.

  Recently, a low-cost fuel cell catalyst that does not require an expensive platinum catalyst has been developed by a reaction in which oxygen is reduced by four electrons to generate water. Non-Patent Document 1 below discloses that a catalyst having a chalcogen element is excellent in 4-electron reducibility and suggests application to a fuel cell.

  Similarly, Patent Document 1 below discloses an electrode catalyst composed of at least one transition metal and a chalcogen as a platinum substitute catalyst, wherein Ru is used as the transition metal, and S or Se is used as the chalcogen. Yes. Here, it is disclosed that the Ru: Se molar ratio is in the range of 0.5 to 2 and the stoichiometric number n of (Ru) nSe is 1.5 to 2.

  Patent Document 2 listed below discloses a fuel cell catalyst material having a transition metal selected from Fe or Ru, a nitrogen-containing organometallic transition complex, and a chalcogen component such as S as a Pt substitute catalyst. .

  Non-Patent Document 1 below discloses a Mo—Ru—Se ternary electrode catalyst and a synthesis method thereof.

  Furthermore, Non-Patent Document 2 below discloses Ru-S, Mo-S, Mo-Ru-S binary and ternary electrode catalysts, and a synthesis method thereof.

  Further, Non-Patent Document 3 below discloses Ru—Mo—S and Ru—Mo—Se ternary chalcogenide electrode catalysts.

JP-T-2001-502467 JP-T-2004-532734 Electrochimica Acta, vol. 39, no. 11/12, pp. 1647-1653, 1994 J. et al. Chem. Soc. Faraday Trans. , 1996, 92 (21), 4311-4319. Electrochimica Acta, vol. 45, pp. 4237-4250, 2000

  The catalysts described in Patent Document 1 and Non-Patent Documents 1, 2, and 3 did not have sufficient four-electron reduction performance.

In addition, the conventional catalyst manufacturing method uses harmful substances such as Fe carbonyl and Ni carbonyl. For example, in the method described in Non-Patent Document 1, since the following problems occur due to limited raw materials used, development of a synthesis method by another method has been desired.
(1) Fe carbonyl and Ni carbonyl used as raw materials are highly toxic. Some of these raw materials have low recyclability.
(2) Metals that can be carbonylated are limited to Group 6 to 10 elements, and transition metals that cannot be carbonylated cannot be used as catalyst constituents, and catalyst development has been limited.
(3) For the reason of (1), it is difficult to discard the remaining raw materials after catalyst synthesis, and it is difficult to recycle the waste liquid remaining in the synthesized words.

  Therefore, the present invention is a fuel cell electrode catalyst which is an alternative to platinum, has a high four-electron reduction performance and is highly active, and does not use harmful substances in its production method, and is safe and highly recyclable. It aims at providing the manufacturing method of.

  The present inventors have found that the above problems can be solved by employing (1) a chalcogen-based catalyst containing a specific transition element and (2) a specific production process, and have reached the present invention.

That is, first, the present invention relates to a fuel comprising a ternary chalcogenide represented by M ₁ M ₂ X (M ₁ is Ru, M ₂ is Fe and / or Ni, and X is at least one chalcogen element). It is an electrode catalyst for batteries.

  As the chalcogen element, one or more selected from sulfur (S), selenium (Se), and tellurium (Te) are preferably exemplified.

  More specifically, the fuel cell electrode catalyst of the present invention is preferably exemplified by a Ru-Fe-Se three-way catalyst or a Ru-Ni-Se three-way catalyst.

Second, the present invention provides a fuel cell electrode catalyst represented by the above M ₁ M ₂ X (M ₁ is Ru, M ₂ is Fe and / or Ni, and X is at least one chalcogen element). An invention of a method comprising: mixing one or more compounds selected from an Fe nitrate compound, an Ni nitrate compound, an Fe hydrochloric acid compound, and an Ni hydrochloric acid compound, an alcohol, and water; and stirring the mixture A step of adding a Ru chalcogen compound, a step of reducing the Fe and / or Ni compound by adding a reducing agent while stirring the mixture, a step of filtering and washing the product, and heat treating the filtrate The process of carrying out.

  In the method for producing a fuel cell electrode catalyst of the present invention, the chalcogen element is preferably exemplified by one or more selected from sulfur (S), selenium (Se), and tellurium (Te).

  In the method for producing a fuel cell electrode catalyst of the present invention, isopropanol is preferably exemplified as the alcohol, and hydrazine is preferably exemplified as the reducing agent.

  Moreover, as said heat processing, 10 minutes-5 hours are preferable at 400-600 degreeC, and 30 minutes-2 hours are more preferable at 480-520 degreeC.

  In the method for producing a fuel cell electrode catalyst of the present invention, the Fe raw material and / or Ni raw material are nitrates and chlorides, and Fe and / or Ni are present in an ionic state in the waste liquid, so that the recovery is easy. On the other hand, when metal carbonyl is used as in the conventional method, the metal is present in zero valence, and is difficult to recover. Therefore, it is preferable in view of environmental problems to further provide a step of recovering Fe ions and / or Ni ions remaining in the waste liquid generated by the method for producing the fuel cell electrode catalyst.

  Specifically, as a publication for recovering Fe ions and / or Ni ions remaining in the waste liquid, use is made of a plating method, a reductive crystallization method, and a zeolite after making the pH of the solution 7.0 or higher to be a hydroxide. One or more of the methods of recovering in this manner are preferably exemplified.

Third, the present invention is an invention of a fuel cell comprising the above fuel cell electrode _{catalyst, M 1 M 2 X (M} 1 is Ru, _{M 2} is Fe and / or Ni, X is at least one It is a fuel cell provided with the electrode catalyst for fuel cells represented by (chalcogen element).

  The fuel cell electrode catalyst of the present invention and the fuel cell electrode catalyst produced by the method of the present invention are less expensive, have higher four-electron reduction performance and higher activity than conventional transition metal-chalcogen element catalysts. In addition to being a substitute for the conventional platinum catalyst, no harmful substances such as Fe carbonyl and Ni carbonyl are used in the production process and no harmful substances are generated.

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

[Example 1: Preparation of catalyst]
Using the raw materials shown in Table 1, a catalyst was prepared according to the reaction scheme shown in FIG. Note that RuSe / C was adjusted by a conventional method.

  2 and 3 show the evaluation results of the oxygen reducing ability of the catalyst synthesized in Example 1. FIG. 2 and 3, it can be seen that the fuel cell electrode catalyst comprising Ru and at least one chalcogen element containing iron (Fe) or nickel (Ni) as a transition metal element is highly active.

  The performance evaluation method is as follows.

[Evaluation equipment]
As shown in FIG. 4, the evaluation was carried out using a three-electrode electrochemical cell. As the electrolytic solution, 0.1 mol / L perchloric acid was used.

[Electrode fabrication method]
FIG. 5 shows an electrode manufacturing method. Catalyst ink was blended in such a way that Nafion was 0.1 with respect to 1 by weight. The ink composition is 0.05 g of catalyst, 1.0 g of 0.5 wt% Nf solution, and 2.0 g of ethanol. (1) Mix with Nf solution and ethanol, (2) Disperse with ultrasonic waves, (3) Drop catalyst ink onto glassy carbon disk electrode and let it dry naturally.

[Evaluation procedure]
Table 2 shows the current evaluation procedure. The electrode rotation speed in Table 2 below indicates the rotation speed of the working electrode in FIG. The index representing the activity is oxygen reduction current = (reduction current measured by O ₂ electrochemical measurement in Table 1) − (reduction current measured by N ₂ electrochemical measurement in Table 1).

[Example 2: Preparation of catalyst]
In the method for synthesizing the Mo—Ru—Se ternary electrode catalyst disclosed in Non-Patent Document 1, the following problems arise because the precursors used are limited. For this reason, it is necessary to pioneer synthesis methods by other routes.
(1) Some metal carbonyls used as precursors have high toxicity such as nickel carbonyl and iron carbonyl. For example, Ni carbonyl is designated as a poison by MSDS, and Fe carbonyl is described as a compound having a great influence on human health in a safety data sheet.
(2) The metals that can be carbonylated are limited to Group 6 to 10 elements, and transition metals that cannot be carbonylated cannot be used as the catalyst constituent composition.

  Therefore, Fe—RuSe / C (20 wt%) was adjusted by the method of the present invention shown in FIG. 1 instead of the conventional synthesis method shown in FIG. Table 3 shows the evaluation results of the redox ability of the present invention and the conventional method.

  From the results in Table 3, it can be seen that the oxidation-reduction ability of the catalyst produced by the production method of the present invention is remarkably improved as compared with the catalyst produced by the conventional method.

  The fuel cell electrode catalyst of the present invention and the fuel cell electrode catalyst produced by the method of the present invention have high four-electron reduction performance and high activity as compared with conventional transition metal-chalcogen element-based catalysts. It can be an alternative to the platinum catalyst. Moreover, it is preferable at the point which does not use harmful substances, such as Fe carbonyl and Ni carbonyl. Furthermore, the present invention is a highly recyclable method. This contributes to the practical application and spread of fuel cells.

The chart which shows the Fe-RuSe / C synthesis method of this invention. The evaluation result of the oxygen reduction ability of the catalyst synthesize | combined in Example 1 is shown. The other evaluation result of the oxygen reduction ability of the catalyst synthesize | combined in Example 1 is shown. An evaluation apparatus is shown. An electrode manufacturing method will be described. The chart which shows the conventional Fe-RuSe / C synthesis method.

Claims (12)

An electrode catalyst for a fuel cell represented by M ₁ M ₂ X (M ₁ is Ru, M ₂ is Fe and / or Ni, and X is at least one chalcogen element).   2. The fuel cell electrode catalyst according to claim 1, wherein the chalcogen element is at least one selected from sulfur (S), selenium (Se), and tellurium (Te).   The fuel cell electrode catalyst according to claim 1 or 2, which is a Ru-Fe-Se three-way catalyst or a Ru-Ni-Se three-way catalyst. A method for producing an electrode catalyst for a fuel cell represented by M ₁ M ₂ X (M ₁ is Ru, M ₂ is Fe and / or Ni, and X is at least one chalcogen element), which comprises an Fe nitrate compound, Ni A step of mixing one or more compounds selected from a nitric acid compound, a Fe hydrochloric acid compound and a Ni hydrochloric acid compound, an alcohol and water, a step of adding a Ru chalcogen compound while stirring the mixture, and the mixture Of a fuel cell electrode catalyst comprising a step of reducing the Fe and / or Ni compound by adding a reducing agent while stirring, a step of filtering and washing the product, and a step of heat treating the filtrate Method.   The method for producing an electrode catalyst for a fuel cell according to claim 4, wherein the chalcogen element is at least one selected from sulfur (S), selenium (Se), and tellurium (Te).   The method for producing an electrode catalyst for a fuel cell according to claim 4 or 5, wherein the alcohol is isopropanol.   The method for producing an electrode catalyst for a fuel cell according to any one of claims 4 to 6, wherein the reducing agent is hydrazine.   The method for producing a fuel cell electrode catalyst according to any one of claims 4 to 7, wherein the heat treatment is performed at 400 to 600 ° C for 10 minutes to 5 hours.   The method for producing a fuel cell electrode catalyst according to any one of claims 4 to 7, wherein the heat treatment is performed at 480 to 520 ° C for 30 minutes to 2 hours.   10. The fuel cell according to claim 4, further comprising a step of recovering Fe ions and / or Ni ions remaining in the waste liquid generated by the method for producing a fuel cell electrode catalyst. A method for producing an electrode catalyst.   The step of recovering Fe ions and / or Ni ions remaining in the waste liquid includes a plating method, a reductive crystallization method, and a method of recovering using a zeolite after converting the pH of the solution to 7.0 or higher to be a hydroxide. It is 1 or more types of these, The manufacturing method of the electrode catalyst for fuel cells of Claim 10 characterized by the above-mentioned.   A fuel cell comprising the fuel cell electrode catalyst according to any one of claims 1 to 3.

Images