KR20040025987A - Manufacturing method of Pt catalyst for electrode utilizing carbon nanotube - Google Patents

Abstract

PURPOSE: Provided is a process for producing a platinum catalyst for an electrode of a fuel cell by using a carbon nano tube, which can improve the reactivity of the electrode of the fuel cell by reducing a particle diameter of the platinum catalyst to several nanometer or less. CONSTITUTION: The process contains the steps of: depositing a platinum(Pt) membrane on a silicon substrate, wherein the platinum membrane has a thickness of 10-50 angstrom; etching the platinum membrane with an etching gas to roughen the surface of the platinum membrane, wherein the etching gas is ammonia(NH3); growing the carbon nano tube to adsorb the platinum catalyst uniformly to the carbon nano tube by precipitating the platinum catalyst having a size of several tens nanometer or less by supplying a reactive gas and the etching gas to the platinum membrane.

Description

Manufacturing method of platinum catalyst for electrode of fuel cell using carbon nanotubes {Manufacturing method of Pt catalyst for electrode utilizing carbon nanotube}

The present invention relates to a method for producing a catalyst for an electrode of a fuel cell, and more particularly to a method for producing a platinum catalyst for an electrode of a fuel cell.

A fuel cell is a power generation element that converts chemical energy of fuel into electrical energy. Recently, research on using a fuel cell as a power supply source for automobiles, houses, and mobile devices has been conducted.

1 is a view schematically showing the structure of a fuel cell. Referring to FIG. 1, a fuel cell includes a membrane electrode assembly (MEA) and a fuel supply container 17 in which an anode 11 and a cathode 13 electrode are disposed in a cell, and an electrolyte membrane 15 is arranged therebetween. ) And an air supply container 19. In the anode 11, hydrogen (H ₂ ) provided from the fuel of the fuel supply container (17) becomes hydrogen ions (H ⁺ ) by the reaction formula as shown in Formula 1, which loses electrons, and is introduced into the electrolyte membrane (15).

H_2-> 2H ^ + + 2e ^-

The cathode 13 generates water by the formula (2) from hydrogen ions (H ⁺ ) supplied from the electrolyte membrane 15, oxygen supplied from the air of the air supply vessel 19, and electrons supplied from the anode 11. .

That is, the entire cell reaction occurring in the entire fuel cell from Formulas 1 and 2 may be represented as in Formula 3.

In order to improve energy density and output voltage in fuel cells, researches on electrodes, fuels, and electrolyte membranes are being actively conducted. In particular, attempts have been made to increase the reactivity of catalysts to improve the conductivity of electrodes. . The performance of the electrode is greatly influenced by the ease of mass transfer, such as the diffusion of reactants into the catalyst bed and the discharge of reaction products, which improves as the reaction surface area of the catalyst increases. Therefore, in order to increase the reactivity of the catalyst present in the electrode, it is necessary to reduce the particle diameter of the catalyst to a size of several nm to increase the reaction surface area.

Therefore, the technical problem to be achieved by the present invention is to improve the above-described problems of the prior art, in particular, by reducing the particle diameter of the platinum catalyst to a size of several nm or less of the fuel cell that can improve the reactivity of the electrode of the fuel cell It is to provide a method for producing a platinum catalyst for the electrode.

1 is a view schematically showing the structure of a fuel cell,

2 is a flowchart showing a platinum catalyst manufacturing method according to an embodiment of the present invention;

Figure 3a to 3d is a process chart showing a platinum catalyst manufacturing method according to an embodiment of the present invention,

Figure 4 is an apparatus showing a reaction apparatus used in the platinum catalyst manufacturing method according to an embodiment of the present invention,

Figure 5 is a SEM photograph showing the carbon nanotubes adsorbed platinum catalyst prepared by the platinum catalyst manufacturing method according to an embodiment of the present invention,

6 is an enlarged TEM photograph of a carbon nanotube adsorbed by a platinum catalyst prepared by a platinum catalyst manufacturing method according to an embodiment of the present invention;

Figure 7 is a TEM photograph of an enlarged carbon nanotubes adsorbed platinum catalyst prepared by the platinum catalyst manufacturing method according to an embodiment of the present invention,

8 is an enlarged TEM photograph of a carbon nanotube adsorbed by a platinum catalyst prepared by a platinum catalyst manufacturing method according to an embodiment of the present invention.

<Code Description of Main Parts of Drawing>

11; Anode 13; Cathode

15; Electrolyte membrane 17; Fuel supply container

19; Air supply container 21; Load

31; Substrate 33; Platinum film

35; NH ₃ plasma 37; NH ₃ and C ₂ H ₂ Mixed Plasma

41; Heater 42; Vacuum pump

43; Lower electrode 45; Upper electrode

47; Vacuum tube 49; Reaction vessel

The present invention to achieve the above technical problem,

Depositing a platinum (Pt) film on a substrate; and

Etching the platinum film with an etching gas to roughen the surface of the platinum film; and

And supplying a reactive gas and an etching gas to the platinum film to precipitate a platinum catalyst having a size of several tens of nm or less and to grow the carbon nanotubes to be uniformly adsorbed onto the carbon nanotubes. It provides a method for producing a platinum catalyst for an electrode of a fuel cell.

In the first step, the platinum film is preferably formed to a thickness of about 10 to 50Å.

In the first step, the substrate is formed of silicon.

In the first step, it is preferable to further form a Ti film at the interface between the substrate and the platinum film.

In the second step, the etching gas is preferably ammonia (NH ₃ ).

In the second step, the ammonia is preferably injected into the upper surface of the platinum film at a flow rate of about 240 sccm at a temperature of about 310 ° C. for about 1 minute.

In the second step, it is preferable to form the plasma by applying electrical energy of about 550V and 0.04A to the ammonia.

In the third step, the reactive gas is preferably ethylene (C ₂ H ₂ ).

In the third step, it is preferable to inject about 15 minutes into the ethylene at a flow rate of about 60 sccm at a temperature of about 520 ℃.

In the third step, it is preferable to form the plasma by applying electrical energy of 620V and 0.12A to the ethylene and ammonia.

In the first step, the platinum film is deposited by chemical vapor deposition or monolayer deposition.

In the second step, the platinum film is preferably etched using the RIE method.

In the third step, it is preferable to grow the carbon nanotubes by plasma chemical vapor deposition.

In the third step, the platinum catalyst is preferably precipitated in the size of 3 to 5nm.

The present invention provides a method for growing a carbon nanotube on the upper surface of a metal film and allowing the platinum catalyst to be adsorbed and grown on the carbon nanotube to produce a platinum catalyst used for an electrode of a fuel cell with a small size of several nm or less. do.

Hereinafter, a platinum catalyst manufacturing method used for an electrode of a fuel cell according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a flow chart showing a platinum catalyst manufacturing method according to an embodiment of the present invention, Figure 3a to 3d is a process chart showing a platinum catalyst manufacturing method according to an embodiment of the present invention.

2 and 3A, in operation 111, a platinum (Pt) layer 33 is deposited on the upper surface of the silicon substrate 31. The platinum film Pt is deposited using a general chemical vapor deposition (CVD) or atomic layer deposition (ALD) method.

Next, referring to FIGS. 2 and 3B, in step 113, ammonia (NH ₃ ) 35 is injected into the upper surface of the platinum film 33 to form plasma to pre-etch the surface of the platinum film 33. By etching, the platinum film 33 is roughened to roughen the surface. At this time, the ammonia 35 is injected at a flow rate of about 200 to 300 sccm, and is injected for about 1 minute at a temperature of about 250 to 350 ° C., and 500 to 600 V and 0.02 to 0.06 A of electrical energy are added to the ammonia 35 to plasma. To form. By roughening the surface of the platinum film 33, the platinum catalyst 32 particles can be easily precipitated by weakening the bonding force with the surface of the platinum film 33.

In the 115th step, acetylene (C ₂ H ₂ ) and ammonia (NH ₃ ) are injected into the top surface of the roughened platinum film 33 to grow a carbon nanotube (CNT) 30. At this time, the flow rate of acetylene is about 50 ~ 70sccm, and the injection time of acetylene and ammonia is about 12 ~ 17 minutes, and it is formed by plasma giving electric energy of about 570 ~ 6700V, 0.08 ~ 0.16A and forming carbon nanotubes (30 Grow). The growth temperature of the carbon nanotubes 30 is suitable about 500 ~ 550 degrees.

Herein, the carbon nanotubes 30 are grown by plasma enhanced chemical vapor deposition (PECVD). As shown in the drawing, the carbon nanotubes 30 grow on the surface of the platinum film 33, and on the other hand, the platinum catalysts 32 precipitated by the etching gas are adsorbed on the carbon nanotubes 30 and grow. The platinum catalyst 32 is formed in a small size of several tens to several tens of nm, and the surface area per unit weight increases, while the platinum catalyst 32 is uniformly dispersed in the lattice structure of the carbon nanotubes 30 so that agglomeration does not occur. 32) is made.

In the plasma chemical vapor deposition method, an acetylene gas is injected between two electrodes of a reactor in which a metal catalyst is present, the gas is glow discharged by a direct current or a high frequency electric field, transformed into a plasma, and the energy is deposited on the electrode. It is a method of growing carbon nanotubes. Plasma refers to a collection of generated ions and electrons when free electrons generated by glow discharge get enough energy to collide with gas molecules. In addition to the above-described plasma chemical vapor deposition, carbon nanotubes can be grown using an arc discharge, laser vaporization, thermal chemical vapor deposition, vapor phase growth, and the like. Can be.

In chemical vapor deposition, methane (CH ₄ ), acetylene (C ₂ H ₂ ), and carbon monoxide (CO) are used as reaction gases for depositing carbon nanotubes, which are hydrogen (H ₂ ) or ammonia (NH _3). Mixed with such etchant gases. Methane in the reaction gas can produce carbon nanotubes having good properties when using high energy plasma, and acetylene can deposit carbon nanotubes even at relatively low temperatures.

In the present invention, an ammonia plasma is used as an etching gas and ethylene plasma is used as a reactive gas.

In step 117, the carbon nanotubes 30 started to grow in step 115 and the platinum catalyst 32 precipitated from the platinum film is adsorbed on the surface or the inner surface thereof and continues to grow. When the carbon nanotubes 30 are grown, the particle size of the platinum catalyst 32 adsorbed to the carbon inside and on the surface of the carbon nanotubes 30 is about 5 nm, so that the carbon nanotubes 30 can be efficiently used in a fuel cell.

According to the type of electrolyte used, the fuel cell may be an alkali type (Alkali Fuel Cell), a phosphoric acid type (PAFC; Phosphoric Acid Fuel Cell), a molten carbonate type (MCFC; Melted Carbonate Fuel Cell), or a solid oxide type (SCFC; Solid C? Fuel Cell) and Solid Polymer Electrolyte Fuel Cell (PEMFC). Here, fuel cells requiring platinum catalysts are alkali type, phosphoric acid type, and solid polymer electrolyte type fuel cells.

Alkaline fuel cell uses KOH solution as electrolyte and porous nickel with platinum catalyst as electrode, phosphoric acid fuel cell uses phosphoric acid (H ₂ PO ₄ ) as electrolyte and porous nickel or graphite with platinum catalyst Used as an electrode. The solid polymer electrolyte fuel cell uses a polymer electrolyte membrane (Nafion, etc.) as an electrolyte, and PTFE having a platinum catalyst as an electrode.

Molten carbonate fuel cell uses molten carbonate (Li ₂ CO ₃ + K ₂ CO ₃ ) as electrolyte and porous nickel as an electrode, but no platinum catalyst, and solid oxide fuel cell also uses YSZ (ZrO ₂ + Y ₂ O ₃ ) is used as electrolyte and nickel oxide is used as electrode, but platinum catalyst is not used.

Therefore, the platinum catalyst prepared by the platinum catalyst manufacturing method according to the embodiment of the present invention can be used in the above-described alkali type, phosphoric acid type solid polymer electrolyte type electrode.

4 is a reaction apparatus used in the platinum catalyst production method according to the embodiment of the present invention.

Referring to FIG. 4, a heater 41 is disposed on a bottom surface of the reaction vessel 49, and a lower electrode 43 is provided on an upper portion thereof. The multilayer film structure of the substrate 31 and the platinum film 33 is provided on the upper surface of the lower electrode 43, and the upper electrode 45 is positioned on the upper portion of the multilayer film structure opposite to the lower electrode 43. The reaction vessel 49 is provided with a supply pipe 47 through which the etchant gas and the reactive gas are supplied from the outside, and a vacuum pump 42 through which the gases are discharged after the reaction. The RF (Radio Frequency) generator provided at the outside has an upper electrode. It is connected to the 45 and the lower electrode 43 to transfer electrical energy. The upper electrode 45 may be formed in a mesh shape to supply a gas injected from the supply pipe 47 to the upper portion of the platinum film 33.

Table 1 below shows experimental conditions of carrying out the platinum catalyst preparation method according to the embodiment of the present invention using the reactor shown in FIG.

NH ₃ plasma etching CNT growth with C ₂ H ₂ + NH ₃ plasma NH ₃ (sccm) Plasma Power (V / A) Minutes Etching Temperature (℃) C ₂ H ₂ Flow rate (sccm) Plasma Power (V / A) Minutes Growth temperature (℃) 240 550 / 0.04 One 310 60 620 / 0.12 15 520

TABLE 1

When the ammonia (NH ₃ ) gas is supplied to the upper surface of the platinum film 33 as the etching gas, the temperature of the vacuum vessel 49 is maintained at about 310 ° C. and flows for about 1 minute at a flow rate of about 240 sccm. At this time, the plasma power for the glow discharge is about 550V / 0.04A.

The surface of the platinum film 33 is roughened as a previous step for forming a platinum catalyst, and then ethylene (C2H2) gas is selected as a reactive gas and supplied to the upper surface of the platinum film 33 together with the ammonia gas, which is an etching gas.

At this time, the temperature for growing carbon nanotubes in the reaction vessel 49 is about 520 ° C, and the flow rate of ethylene gas is supplied to the upper surface of the platinum film 33 for about 15 minutes at about 60 sccm. Electric energy for plasma formation of ethylene gas and ammonia gas is supplied to be about 620V / 0.12A.

The carbon nanotubes 30 are formed on the surface of the platinum film 33 and start to grow. The platinum catalyst 32 etched by the etching gas from the platinum film 33 is formed by the growth of the carbon nanotubes 30. Together and evenly dispersed in the entire structure of the carbon nanotubes (30). Inside the carbon nanotubes 30, particles of platinum catalyst 32 having a size of about 2 to 30 nm are generated and adsorbed.

As the etching time by the ammonia plasma increases, the growth density of the carbon nanotubes decreases, whereas as the amount of ammonia and ethylene mixed plasma increases, the etching increases and the density of the carbon nanotubes increases. In addition, as the carbon nanotube growth time increases, the decomposition of acetylene increases and the carbon nanotube length increases.

In the case of depositing a titanium (Ti) film on the upper surface of the substrate, and then depositing a platinum film on the upper surface of the substrate and growing carbon nanotubes, the weak bonding force between the platinum and titanium decreases the area of platinum agglomeration nuclei and increases the diffusion rate, thereby reducing the size of platinum. Nanoparticles can be produced in large quantities.

In order to make more platinum catalyst 32 of smaller size and to distribute it evenly in the carbon nanotubes, it is necessary to increase the roughness of the surface of the platinum film 33 in the linear etching process and increase the amount of etching and reactive gases. Conditions for growing carbon nanotubes are required. Experimental conditions described above for such growth conditions may be one example, but are not limited thereto.

SEM (Scanning Electron Microscopy) photographs of carbon nanotubes and platinum catalysts grown under these experimental conditions are shown in FIG. 5.

Referring to FIG. 5, it can be seen that several hundred nm sized carbon nanotubes are grown vertically and platinum catalyst is deposited between the carbon nanotubes.

FIG. 6 is a transmission electron microscopy (TEM) photograph showing an enlarged view of one of the carbon nanotubes shown in FIG. 5. Numerous platinum catalysts appear as black dots in carbon nanotubes.

FIG. 7 is an enlarged view of the carbon nanotubes of FIG. 6. In the figure, it can be seen that the platinum catalyst adsorbed on the surface of the carbon nanotubes is black, and the platinum catalyst adsorbed therein is blurred.

FIG. 8 is an enlarged TEM photograph of the carbon nanotube shown in FIG. 7. The platinum catalyst adsorbed on the outside has a diameter of about 5.27 nm and the platinum catalyst adsorbed on the inside has a diameter of about 3.33 nm. You can see that.

From this, the electrode catalyst manufacturing method of the fuel cell of the present invention precipitates the platinum catalyst so as to have a diameter of about 3 to 4 nm, thereby increasing the surface area per unit weight of the platinum catalyst applied to the electrode used in the fuel cell, thereby improving the reactivity of the electrode. By increasing the overall performance of the fuel cell can be improved.

While many details are set forth in the foregoing description, they should be construed as illustrative of preferred embodiments, rather than to limit the scope of the invention.

For example, a person having ordinary knowledge in the technical field to which the present invention belongs may have several nm by a method similar to the platinum catalyst manufacturing method described above in the process of growing carbon nanotubes according to the technical idea of the present invention. It will be able to precipitate in size. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the technical spirit described in the claims.

As described above, an advantage of the method of manufacturing a platinum catalyst for an electrode of the fuel cell of the present invention is that a large amount of platinum catalyst can be produced in a size of several nm or less, and thus used in an electrode of a fuel cell, thereby improving the reactivity of the electrode of the fuel cell, thereby improving overall fuel The performance of the battery can be improved.

Claims (14)

Depositing a platinum (Pt) film on a substrate; Etching the platinum film with an etching gas to roughen the surface of the platinum film; And supplying a reactive gas and an etching gas to the platinum film to precipitate a platinum catalyst having a size of several tens of nm or less and to grow the carbon nanotubes to be uniformly adsorbed onto the carbon nanotubes. Method for producing a platinum catalyst for an electrode of a fuel cell. The method of claim 1, wherein in the first step, The platinum film is a platinum catalyst manufacturing method for an electrode of a fuel cell, characterized in that formed in a thickness of about 10 to 50Å. The method of claim 1, wherein in the first step, The substrate is a method of producing a platinum catalyst for electrodes of a fuel cell, characterized in that formed of silicon. The method of claim 1, wherein in the first step, And a titanium (Ti) film is further formed at the interface between the substrate and the platinum film. The method of claim 1, wherein in the second step, Wherein the etching gas is ammonia (NH ₃ ) The platinum catalyst manufacturing method for an electrode of a fuel cell, characterized in that. The method of claim 5, wherein in the second step, And ammonia is injected into the upper surface of the platinum film at a flow rate of about 240 sccm at a temperature of about 310 ° C. for about 1 minute. The method of claim 6, wherein in the second step, A method of manufacturing a platinum catalyst for an electrode of a fuel cell, characterized in that the ammonia is applied to electrical energy of about 550 V and about 0.04 A to form a plasma. The method of claim 7, wherein in the third step, The reactive gas is ethylene (C ₂ H ₂ ) The method for producing a platinum catalyst for an electrode of a fuel cell, characterized in that. The method of claim 8, wherein in the third step, Method for producing a platinum catalyst for an electrode of a fuel cell, characterized in that the ethylene is injected for about 15 minutes at a flow rate of about 60sccm at a temperature of about 520 ℃. The method of claim 9, wherein in the third step, A method of manufacturing a platinum catalyst for an electrode of a fuel cell, characterized in that the ethylene and ammonia are applied to electric energy of 620V and 0.12A to form a plasma. The method of claim 1, wherein in the first step, The platinum film is a method for producing a platinum catalyst for the electrode of a fuel cell, characterized in that the deposition by chemical vapor deposition or monolayer deposition method. The method of claim 1, wherein in the second step, Platinum catalyst manufacturing method for the electrode of a fuel cell, characterized in that the platinum film is etched using a RIE method. The method of claim 1, wherein in the third step, A method for producing a platinum catalyst for an electrode of a fuel cell, wherein the carbon nanotubes are grown using a plasma chemical vapor deposition method. The method of claim 1, wherein in the third step, The platinum catalyst is a platinum catalyst manufacturing method for an electrode of a fuel cell, characterized in that precipitated in the size of 3 to 5nm.