KR100489215B1 - Method for preparing electrocatalyst for fuel cell and electrocatalyst for fuel cell - Google Patents

Abstract

The present invention relates to a method for producing a catalyst for a fuel cell and a catalyst for a fuel cell, and more particularly, to manufacture a catalyst for a fuel cell by supporting a catalyst metal on a nano-frame. In the production method of the present invention, since the catalyst metal is regularly and polydispersed in the size of nanoparticles, it is possible to reduce the amount of expensive catalyst metal used, thereby improving the price competitiveness. In addition, the catalyst of the present invention can improve the efficiency and performance of a fuel cell having the same due to the electrochemical characteristics of the oxidation-reduction active current density is significantly higher than the conventional catalyst for fuel cells.

Description

METHODS FOR PREPARING ELECTROCATALYST FOR FUEL CELL AND ELECTROCATALYST FOR FUEL CELL}

The present invention relates to a method for producing a catalyst for a fuel cell and a catalyst for a fuel cell, and more particularly, to a method for producing a catalyst for a fuel cell and a fuel cell catalyst supporting a catalyst metal on a nano-frame.

A fuel cell is a battery that converts chemical energy generated by oxidation of fuel into electrical energy. The point of using redox is the same as that of a normal chemical cell, but it is a cell reaction in a closed system. Unlike chemical cells, the reactant is continuously supplied from the outside, and the reaction product is continuously removed out of the system.

Fuel cells are classified into gas fuel using fossil raw materials such as methane or natural gas in addition to hydrogen and liquid fuel using methanol or hydrazine. In addition, depending on the type of electrolyte, it is classified into alkali type, phosphoric acid type, molten carbonate type, solid oxide type and solid polymer electrolyte type.

Among them, those having an operating temperature of 300 deg. In addition, according to power generation efficiency, a molten carbonate fuel cell that does not use a noble metal catalyst is referred to as a second generation fuel cell.

In recent years, the most practical approach is the first generation fuel cell, and a phosphate electrolyte fuel cell developed for general civilian use, especially in the US UT, is a good example. This is a hydrogen-air fuel cell using hydrogen gas mainly containing hydrogen reformed fossil fuel and oxygen in the air. In 1988, the Korea Institute of Energy and Resources developed a 5 kW class fuel cell that obtains heat and electricity simultaneously with methanol as its main raw material. In addition, a method of manufacturing an electrode of a direct methanol fuel cell (DMFC) is already known (Korean Patent No. 10-1999-0025037).

The fuel cell is an environmentally friendly reactor in which hydrocarbons or hydrogen react with water to discharge carbon dioxide from the anode, and in the reduction electrode, oxygen in the air reacts with H ⁺ delivered through the electrolyte to discharge water.

Therefore, when the fuel cell is used in automobiles, the pollution problem can be solved, and in addition, since the fuel cell is more efficient than any energy conversion mechanism so far, it is very important in terms of alternative energy for energy depletion.

In addition, the fuel cell is an energy conversion system that can be used for more than 50,000 hours when fuel is supplied without the inconvenience of charging. When using a portable electronic device, the fuel cell can be continuously used conveniently without replacing or recharging the battery. It is expected to account for about 30% of the rechargeable battery market.

In spite of these advantages, however, precious metal catalysts such as platinum and ruthenium are mainly used to produce the catalyst, which is the main material of the electrode, and in the case of low-temperature fuel cells operating at low temperatures near room temperature, an excessive amount of precious metal catalyst has to be used. Due to technical limitations, commercialization is not achieved.

In particular, the catalyst of the redox electrode is used in the form of very fine metal powder or conductive carbon supported on the conductive carbon, and in order to thinly coat the carbon paper or the electrolyte membrane, it is mixed with a binder such as Teflon or Nafion to prepare the electrode. . In this case, the binder used may play a positive role in fixing the catalyst powder or delivering H ⁺ , but may also play a negative role in blocking the fine pores of the porous catalyst and thus rapidly decreasing the utilization of precious metals.

In order to replace existing cells, fuel cells must not only have better price and performance than current products, but also be competitive with new products such as lithium metal batteries being developed.

In order to improve the performance of a fuel cell, fuel cell catalysts of various compositions have been known, and researches to improve the performance of fuel cells by adjusting various metal composition ratios of fuel cell catalysts have been conducted (US Pat. No. 6,284,402).

As part of this effort, the present inventors can manufacture a fuel cell catalyst by carrying a catalyst metal on a nano-frame, thereby adjusting the shape of the fuel cell catalyst to reduce the amount of platinum or ruthenium and to improve performance. By confirming, the present invention was completed.

It is an object of the present invention to provide a method for producing a catalyst for a fuel cell.

Another object of the present invention is to provide a catalyst for a fuel cell according to the production method of the present invention.

The present invention provides a method for producing a catalyst for a fuel cell.

The production method of the present invention is to prepare a catalyst for a fuel cell by supporting a catalyst metal on a nano-frame.

More specifically, the method comprises the steps of: 1) supporting the catalyst metal on the nano mold in the form of silicon oxide; and 2) removing the nano mold. Unlike the process obtained by the manufacturing process, the present invention is carried out in one step process by supporting the metal for the catalyst on the nano-frame, it is more economical, if the process using a conventional heterogeneous catalyst, it can be applied without any additional device change have. The supporting of the catalyst metal may include impregnating the precursor of the catalyst metal in the nano mold in the form of silicon oxide and reducing the precursor of the catalyst metal. Reducing the step may be carried out under a hydrogen atmosphere.

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The nano-frame of the present invention may use the form of silicon oxide, preferably silica / alumina in the form of silica, alumina alone or a mixture thereof.

As the catalyst metal, one selected from the group consisting of platinum, ruthenium, iridium, osmium, rhodium, molybdenum, tungsten, gold, iron and selenium is used. Preferably platinum, ruthenium, or a mixture of platinum-ruthenium (Pt-Ru) is used.

In this case, as precursors of platinum and ruthenium, (NH ₃ ) ₄ Pt (NO ₃ ) ₂ and (NH ₃ ) ₆ RuCl ₃ may be used, respectively, and a weight ratio of 10 to 70% of platinum or platinum-ruthenium in 1 g of the nano-frame. Impregnating (Pt-Ru).

The present invention also provides a catalyst for a fuel cell prepared by supporting a catalyst metal on a nano mold in the form of a silicon oxide.

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At this time, the catalyst for a fuel cell of the present invention is obtained in the form of a metal powder.

The metal powder forms are regularly arranged in a two-dimensional or three-dimensional structure in nanoparticle size.

FIG. 1 is a surface photograph of a metal powder obtained when a catalyst metal is supported on a nanoframe, and a metal precursor, Pt-Ru metal powder, is connected by nanowires and observed in a three-dimensional structure.

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Therefore, in the present invention, the metal powder prepared using the nano-frame is not only simpler than the conventional manufacturing method, but also provides economic advantages, and precious metals such as platinum or ruthenium because the metal is regularly and polydisperse in nanoparticle size. It can reduce the use of, can improve the price competitiveness.

2 is a result of measuring the current-voltage of an electrode-electrolyte assembly of a fuel cell having an anode and a cathode prepared with the catalyst prepared in the present invention, and it can be confirmed that the current density is higher than that of the catalyst used in the prior art. .

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Furthermore, the present invention is a metal powder-type fuel cell catalyst prepared by using a nano-frame coated on carbon paper, and adhered with an electrolyte to be used as an electrode-electrolyte assembly of the fuel cell, thereby improving the efficiency and performance than the conventional It is possible to manufacture fuel cells that exhibit economic advantages.

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

This embodiment is intended to illustrate the present invention in more detail, and the scope of the present invention is not limited to these examples. Those skilled in the art can make modifications or improvements with reference to the present specification without departing from the scope and object of the present invention.

Preparation Example 1 Synthesis of Nano Framework

77.5 g of 1 M sodium hydroxide prepared in advance and 22.5 g of Ludox HS 40 were stirred and mixed at 80 ° C. to be used as a silica source. The prepared silica source, octadecytrimethyl ammonium chloride, and Triton (Triton X-100) were mixed well to make a gel mixture and reacted in an oven at 100 ° C. for 60 hours. After adding a small amount of acetic acid to the result so far, the reaction was further carried out for 40 hours in an oven at 100 ℃ to obtain a nano mold (MCM-48).

Pluronic P123 and tetraethylorthosilicate were dissolved in 1.6 M aqueous hydrochloric acid to prepare nano templates. The reaction was allowed to react for 20 hours at room temperature, further reacted for 24 hours in an oven at 100 ° C., filtered, and dried. The reaction product used was composed of a molar ratio of Pluronic P123: tetraethylorthosilicate: HCl: water = 1: 60: 350: 11400.

Example 1 Preparation of Pt-Ru Metal Powder Using Nano Framework

After firing the nano mold prepared in Preparation Example 1 at 300 ℃, it was prepared by using an evaporator to impregnate 1 g of nano mold Pt (75) Ru (25) (atomic ratio) by weight ratio of 67%. In this case, as precursors of Pt and Ru, (NH ₃ ) ₄ Pt (NO ₃ ) ₂ and (NH ₃ ) ₆ RuCl ₃ were used. After impregnation, Pt-Ru metal powder was prepared by reducing under a hydrogen atmosphere of 300 ° C., dissolving the nano mold using a dilute hydrofluoric acid solution, removing it, and then washing the nano mold.

Example 2 Preparation of Platinum (Pt) Metal Powder Using Nano Framework

After firing the nano mold prepared in Preparation Example 1 at 300 ℃, it was prepared by using an evaporator to impregnate 1% of the nano mold Pt by weight ratio of 67%. In this case, Pt metal powder was prepared in the same manner as in Example 1 except that (NH ₃ ) ₄ Pt (NO ₃ ) ₂ was used as the precursor of Pt.

In the above embodiment, the structural analysis of the metal powder prepared using the nano-frame and the performance as a catalyst for a fuel cell were tested as follows.

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Experimental Example 1 Nanostructure Analysis Experiment

In order to analyze the structure of the catalyst for a fuel cell prepared in the above embodiment, it was carried out using a TEM.

1 is a result of observing the Pt-Ru metal powder prepared by using a nano-frame in Example 1, the Pt-Ru metal powder was observed in a three-dimensional structure connected nanowires. Therefore, the metal produced in the present invention When the powder is used as a catalyst for a fuel cell, by using a catalyst having a surface area similar to that of a conventionally used catalyst and connected in a regular two-dimensional or three-dimensional structure, the amount of binder and the amount of binder in the production of a fuel cell can be reduced. Do not block the micro-pore structure so that more precious metals used can all participate in the reaction. Therefore, the amount of precious metals such as platinum or ruthenium can be reduced.

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Experimental Example 2 Current-Voltage Performance Comparison of Electrode-electrolyte Conjugates Using Fuel Cell Catalysts

Using a Pt-Ru metal powder prepared in Example 2 as an anode and a Pt metal powder as a reducing electrode, a methanol fuel cell was fabricated directly and its performance was measured.

For the preparation of the anode, 2 M methanol was injected, Nafion 15% was added, for the production of the cathode, 500 ml / min of oxygen was added, and Nafion 7% was added. In the assembly preparation, two anodes and a cathode were thermally compressed at 120 ° C. for 2 minutes with a Nafion electrolyte membrane interposed therebetween. The voltage-current of each obtained assembly was measured. At this time, the anode conditions were Pt-Ru metal powder 5 mg / sq.cm, 2 M methanol 2 ml / min and O psig, and the reducing electrode conditions were Pt metal powder 5 mg / sq.cm and oxygen 500 ml /. min and O psig, and the electrolyte used was Nafion 117. Operation temperature was carried out at 40 ℃ and 80 ℃, respectively,

In addition, by using the commercial Pt-Ru and Pt metal powder used in the conventional fuel cell production as the anode and the cathode, the assembly was manufactured in the same manner to measure the performance. The results are shown in FIG. 2 , wherein (a) is used as the catalyst prepared in Examples of the present invention, and (b) is a conventional catalyst.

As shown in FIG. 2 , as a result of measuring the current-voltage of the electrode-electrolyte assembly of the fuel cell having the catalyst prepared in the embodiment of the present invention as an anode and a cathode, the temperature was 40 ° C. over that of a conventional catalyst. And it was confirmed that the current density is high under each temperature condition of 80 degreeC. These results showed that the three-dimensional nano metal catalyst of the present invention showed higher activity, and the nano-sized metal catalyst of the present invention exhibited excellent self-activity but electron / hydrogen or cation / oxygen species in a thin electrode-electrolyte junction structure. By smoothly carrying out mass transfer, the activity of the electrode structure as well as the activity of the catalyst itself can be increased.

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As described above, the catalyst for the fuel cell in the form of metal powder prepared using the nano-frame of the present invention has a regular and polydisperse metal in the nanoparticle size, and has the same surface area as the conventional catalyst, By using a catalyst connected in two or three dimensional structures, the amount of the noble metal used as a catalyst can be reduced by reducing the amount of binder and at the same time the binder does not block the micropore structure, so that all of the used noble metals participate in the reaction. have. At the same time, the efficiency and performance of the fuel cell including the catalyst for fuel cell of the present invention can be further improved.

1 is a structural analysis result of the Pt-Ru metal powder prepared in Example 1 of the present invention,

Figure 2 compares the current-voltage performance of the electrode-electrolyte conjugates for the catalysts prepared in the present invention and conventional commercial catalysts.

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(A) An electrode-electrolyte assembly comprising Pt-Ru prepared in Example 1 of the present invention as an anode and Pt metal prepared in Example 2 as a reducing electrode,

(B) It is an electrode-electrolyte assembly provided with the conventional commercial catalyst.

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Claims (13)

A method of manufacturing a catalyst for a fuel cell, the method comprising the steps of supporting the catalyst metal on the nano-form in the form of silicon oxide and removing the nano-frame. The method of claim 1, wherein the supporting of the catalyst metal comprises impregnating a precursor of the catalyst metal in the nano-frame in the form of silicon oxide and reducing the precursor of the catalyst metal. Manufacturing method. The method of claim 1, wherein the nano mold is in the form of silica, alumina alone or a mixture thereof. The method of claim 1, wherein the catalyst metal is selected from the group consisting of platinum, ruthenium, iridium, osmium, rhodium, molybdenum, tungsten, gold, iron and selenium. The method of claim 4, wherein the catalyst metal is platinum, ruthenium, or a mixture thereof. A catalyst for a fuel cell, which is obtained by supporting a catalyst metal on a nano mold in a silicon oxide form and removing the nano mold. The fuel cell catalyst of claim 6, wherein the fuel cell catalyst is in the form of a metal powder. delete delete delete delete delete delete