KR100965836B1 - Method for preparing metal catalyst comprising fluorine functionalized carbon support - Google Patents

Abstract

In the fuel cell metal catalyst manufacturing method according to the present invention, a method of preparing a carbon-based support having a fluorine functional group introduced therein by performing fluorination treatment directly on a carbon-based support, and carrying a metal on the carbon-based support may produce a metal catalyst. It characterized in that it comprises a step of manufacturing, by controlling the fluorine content introduced into the carbon-based support by changing the fluorination treatment temperature it is possible to improve the electrochemical activity while using less expensive metal catalyst in the metal introduction process.

Fuel cell, fluorine treatment, catalyst carrier, carbon black, mixed metal, catalytic activity, temperature

Description

METHODS FOR PREPARING METAL CATALYST COMPRISING FLUORINE FUNCTIONALIZED CARBON SUPPORT}

The present invention relates to a method for producing a metal catalyst with increased supporting efficiency and electrical activity, and to a fuel cell including the metal catalyst.

A fuel cell is an electrochemical device that converts chemical energy into electrical energy, and has been in the spotlight as a next-generation clean energy generation system in that it is a power supply device having characteristics of high efficiency, high output, and pollution. Fuel cells are similar to ordinary batteries such as batteries and accumulators in that they generate electricity by chemical reactions.However, unlike ordinary batteries, fuel cells do not need to be charged or exchanged because they are supplied with hydrogen and oxygen, which are reactants. It is a kind of power generation device that generates electricity.

Fuel cells can be classified according to the fuel used and the operating temperature. In other words, AFCs (alkaline fuel cells), PAFCs (phosphate fuel cells), MCFCs (molten carbonate fuel cells), SOFCs (high solid oxide fuel cells), PEMFCs (polymer electrolyte fuel cells), DMFCs (direct methanol fuel cells) have. Among various types of fuel cells, PEMFCs and DMFCs can be used as power sources for mobile devices. Among them, the DMFC uses methanol instead of hydrogen as fuel, so the battery can be miniaturized. In addition, by supplying only methanol can increase the use time can be eliminated inconvenience caused by the limitation of the capacity, such as the battery or charging time. In particular, with the explosive growth of the mobile phone population, efforts are being made worldwide to develop a DMFC for battery replacement having this advantage.

In general, an electrocatalyst for a fuel cell has a small metal catalyst particle size and is uniformly dispersed in a support to provide a wide area of catalytic active site and a large surface area where a redox reaction occurs. That is, the electrode catalyst carrier should have a large surface area, large pore volume, and high electrical conductivity. Carbon materials, which are widely used electrode catalyst carriers, have problems such as irregular and wide pore structure, low pore volume, and low electric conductivity. .

In addition, in general, the most commonly used as a catalyst for the anode and anode electrode material of the fuel cell is a noble metal catalyst that is most used as a catalyst. In other words, platinum metal particles, which are representative noble metal catalysts, are supported on a catalyst carrier and used as catalyst electrodes. These precious metal catalysts are very expensive and there is a need to reduce the amount of loading without significantly reducing the electrochemical catalyst activity. Since the raw material for the catalytic reaction is mainly liquid or gaseous phase, the specific surface area per unit weight of the platinum catalyst should be maximized to improve the catalytic activity. The most effective way to do this is to minimize the size of platinum particles. Therefore, the method of supporting the platinum catalyst on carbon and the properties of the carbon material are important for the active area of the platinum catalyst.

Many researches and developments have been made on the method of supporting the metal catalyst on the catalyst support. Carbon materials that are frequently used in the production of catalyst layers include carbon black, activated carbon, carbon nanotubes, etc., in order to improve electrode performance and extend battery life, high performance electrode catalyst layers should be prepared. Therefore, in order to increase the active area of the metal catalyst, the characteristics of the carbon material and the method of supporting the metal catalyst on the carbon material are important.How to prepare the catalyst by activating the carbon black, and coating the catalyst directly on the carbon carrier for the fuel cell And a method of producing an electrode catalyst for methanol fuel cell directly from a platinum alloy using anhydrous metal chloride, etc. have recently been used in fuel cell catalyst synthesis. However, catalysts prepared by these methods have a problem in that activity and dispersibility are not sufficient. In addition, the platinum catalyst for fuel cells adsorbs or poisons CO in the reformed gas, making it difficult to put into practical use, and there are many difficulties in producing the metal catalyst.

Accordingly, the present invention is to provide a method for producing a metal catalyst having excellent supporting efficiency and electrochemical activity, and a metal catalyst prepared through the same.

The present invention also provides a fuel cell having improved performance, including the metal catalyst.

In accordance with an object of the present invention, the present invention provides a method for producing a metal catalyst of a fuel cell, by performing a fluorination treatment directly on the carbon-based support to produce a carbon-based support in which a fluorine functional group is introduced, and the carbon-based support It provides a method for producing a metal catalyst comprising the step of supporting a mixed metal on the support to produce a metal catalyst and a metal catalyst prepared through this.

According to the metal catalyst production method of the present invention, by changing the temperature during the fluorination treatment, it is possible to adjust the amount and particle size of the mixed metal to the carbon-based support.

According to another object of the present invention, the present invention provides a fuel cell comprising a metal catalyst prepared by the above method.

As described above, in the present invention, by introducing fluorine into the carbon-based support, the electrochemical activity can be improved while using less expensive metal catalysts in the process of introducing mixed metals. In addition, when a new fluorine functional group is introduced into the carbon-based support, not only the size of the catalyst can be controlled but also the supporting efficiency of the mixed metal can be increased, thereby increasing the activity of the catalyst and greatly contributing to performance improvement. This method is expected to play an important role in the development of fuel cell catalysts in the future, and further active research into the application of fuel cells will be conducted.

Hereinafter, the present invention will be described in detail.

Method for producing a metal catalyst according to the present invention

(a) performing a fluorination treatment directly on the carbon-based support to prepare a carbon-based support having a fluorine functional group introduced therein; and

(b) preparing a metal catalyst by supporting a metal on the carbon-based support into which the fluorine functional group is introduced.

In the present invention, by introducing fluorine into the carbon-based support through the fluorination treatment, it provides new functionality and provides a site on which a metal can be introduced to the surface. As a result, the supporting efficiency of the metal may be increased, and thus, the electrochemical activity of the catalyst may be improved due to the high supporting efficiency of the metal while using less expensive metal catalyst in the mixed metal introduction process.

The production method according to the present invention may further comprise a step of pretreatment to remove impurities present on the surface before step (a). As such a pretreatment step, a Soxhlet extraction method of extracting and removing impurities such as nonvolatile substances present on the surface of the carbon-based support with a volatile solvent is preferable, and heat-treating and acidifying the carbon-based support under specific conditions (Or alkaline) treatment can also be used as a pretreatment step.

In more detail, the preferred method of the present invention is first subjected to surface fluorination by reacting a carbon-based carrier from which surface impurities are removed through pretreatment with pure fluorine gas in a reactor from which oxygen and moisture are removed. . After dispersing the carbon-based carrier into which the fluorine functional group thus obtained is introduced into a solvent, a mixed metal is added and stirred. After the reducing agent is added and heated, the solid powder is filtered, washed and dried to obtain the final metal catalyst.

In the production method of the present invention, the fluorination treatment for the carbon-based support may be performed for 1 to 30 minutes under 0.01 to 1 MPa, and more preferably for 5 to 15 minutes under 0.01 to 0.2 MPa.

At this time, the fluorine treatment temperature for the carbon-based support is preferably at least 800 ° C, more preferably at least 500 ° C.

If the reaction pressure, temperature and reaction time is lower or less than this, the reaction is not sufficient on the surface of the carbon-based support. On the contrary, if the reaction pressure, temperature and reaction time is higher or higher, the carbon-support is excessively influenced and the reaction degree is changed. There will be no.

The inventors of the present invention found that the amount of fluorine introduced into the carbon-based support is changed by changing the temperature at the time of fluorination treatment, and finally, through the change in the amount of fluorine functional group introduced, which gives new functionality to the carbon-based support, It was found that the loading amount and particle size of the mixed metal can be controlled.

In consideration of the electrochemical activity of the final metal catalyst, the amount of fluorine introduced into the carbon-based support is preferably 5 to 40% by weight, more preferably 10 to 30% by weight, based on the weight of the carbon-based support. desirable.

In addition, the particle size of the metal supported on the carbon-based support is preferably 0.1 to 4.5 nm, which is a range of particle sizes that can increase the activity of the catalyst by increasing the loading level of the metal to the carbon-based support. , The content of the metal supported on the carbon-based support is preferably 2 to 30% by weight based on the weight of the metal catalyst.

The metal to be introduced into the carbon-based support in which fluorine is introduced can be variously selected depending on the use of the metal catalyst.

For example, if used in a fuel cell, it is possible to support a mixed metal of Pt and Ru in a carbon-based support, and in the case of such a mixed metal, the electrochemical activity of the final catalyst depends on the Pt / Ru content. The preferred content for obtaining the activity is preferably 5 to 20 wt% of Pt and 2 to 10 wt% of Ru based on the weight of the final metal catalyst.

In addition, when using a metal element such as ruthenium, tin, rhenium, molybdenum and cobalt together with platinum as a catalyst of the fuel cell, it is possible to control the electron density of the platinum to change the electrode performance, and in combination with these various fuels The catalyst of the battery can be prepared.

The carbon-based support used in the preparation of the metal catalyst of the present invention is preferably carbon black, activated carbon, carbon nanotubes, carbon fibers, graphite, graphite nanofibers, and mixtures thereof.

The metal catalyst prepared by the method of the present invention can be usefully used as an electrode material of a fuel cell.

Briefly describing a fuel cell manufacturing process, a fuel cell includes a polymer electrolyte membrane, an electrode, and a separator plate for constituting a stack. The electrode includes a catalyst layer composed of micropores and a gas diffusion layer composed of macropores supplying a reactor gas thereto. The catalyst layer is formed by combining with a water repellent resin such as a carbon-based carrier carrying a catalyst, and the gas diffusion layer is made of hydrophobic carbon paper that has been water-repellent. The two layers may be combined by a rolling method to form an electrode, and the electrode may be attached to the polymer electrolyte membrane by hot-pressing to manufacture a fuel cell.

Hereinafter, embodiments of the present invention have been described. The following examples are merely examples of the technical idea of the present invention, and the scope of the present invention is not limited thereto.

Carbon black was used as the carbon-based support in the following Comparative Examples and Examples, and the carbon black was purchased from Korea Carbon Black Co., Ltd., having an average diameter of 24 nm, a DBP absorption flow rate of 153 cc / g, and a specific surface area of 112 m. ² / g was used. Carbon black used in the present invention was previously treated with Soxhlet extraction using acetone at 80 ° C. for 3 hours to remove impurities.

Comparative Example 1. Preparation of carbon black without direct fluorination treatment

Carbon black treated with Soxhlet extraction to remove impurities without fluorination was named CB-0.

Example 1. Preparation of carbon black subjected to direct fluorination treatment: Fluorination treatment temperature Room temperature

Fluxization was performed on carbon black from which impurities were removed by Soxhlet extraction. Fluorine gas was used as a 99.8% purity product containing a small amount of HF and nitrogen, and used to remove HF by passing NaF pellet heated at a temperature of 100 ℃ or more before the reaction to remove impurities. After the reaction, fluorine gas was removed using an Al ₂ O ₃ pellet. Since fluorine gas is generally highly reactive with metal materials, the material of the reactor is made of stainless steel plate, and a nickel boat is used as the reactor. The experiment was performed after purging with pure nitrogen gas for 1 hour to remove oxygen and water in the reactor and maintaining it at room temperature before the experiment. The fluorine gas was filled in a buffer tank and allowed to mix uniformly for 1 day. Fluorine-containing carbon black was prepared by surface fluorination treatment by maintaining the fluorine gas pressure ratio at 0.1 MPa at a constant temperature for 10 minutes. The finally obtained carbon black was named CB-RT.

Example 2. Preparation of carbon black subjected to direct fluorination treatment: fluorination treatment temperature 100 캜

Fluoride Carbon obtained finally by the same method as in Example 1 except that the surface fluorination treatment by maintaining the gas pressure ratio at 0.1 MPa constant and maintaining the carbon black fluorination treatment temperature at 100 ℃ for 10 minutes Black was named CB-100.

Example 3. Preparation of carbon black subjected to direct fluorination treatment: fluorination treatment temperature of 300 deg.

Fluoride Carbon obtained finally in the same manner as in Example 1, except that the surface fluorination treatment by maintaining the gas pressure ratio at 0.1 MPa constant and maintaining the carbon black fluorination treatment temperature at 300 ℃ for 10 minutes Black was named CB-300.

Example 4 Preparation of Carbon Black Directly Fluoridated: 400 ° C. Fluorination

Fluoride Carbon obtained finally in the same manner as in Example 1, except that the surface fluorination treatment by maintaining the gas pressure ratio at 0.1 MPa constant and maintaining the carbon black fluorination treatment temperature at 400 ℃ for 10 minutes Black was named CB-400.

Comparative Example 2 Metal Catalyst Support Using Carbon Black Without Direct Fluorination Treatment

125 mg of carbon black was added to 25 ml of distilled water as a catalyst carrier and dispersed for 20 minutes using an ultrasonic generator. And 58.3 mg of H ₂ PtCl ₆ and 30 mg of RuCl ₆ were dissolved in distilled water, and then slowly introduced into the carbon dispersion solution and stirred. Thereafter, 50 ml of a 5M NaOH solution was added for pH control, followed by stirring for 4 hours. HCHO (37%, 0.75 mL), a reducing agent of this solution, was added and heated at 110 ° C. for 2 hours. All manufacturing processes were carried out in an argon gas atmosphere, the solid powder was filtered, washed with distilled water, dried at 80 ° C. for 24 hours, and the resulting catalyst was named PtRu / CB-0.

Example 5 Metal Catalyst Support Using Carbon Black Fluorinated at Room Temperature

Except for using the CB-RT of Example 1 as a catalyst carrier, the metal catalyst was carried in the same manner as in Comparative Example 2, and the resulting catalyst was named PtRu / CB-RT.

Example 6 Metal Catalyst Support Using Carbon Black Fluorinated at 100 ° C

Except for using the CB-100 of Example 2 as a catalyst carrier, the metal catalyst was carried in the same manner as in Comparative Example 2, and the final catalyst was named PtRu / CB-100.

Example 7 Metal Catalyst Support Using Carbon Blacks Fluorinated at 300 ° C

Except for using the CB-300 of Example 3 as a catalyst carrier, the metal catalyst was carried in the same manner as in Comparative Example 2, and the final catalyst was named PtRu / CB-300.

Example 8 Metal Catalyst Support Using Carbon Black Fluorinated at 400 ° C

Except for using the CB-400 of Example 3 as a catalyst carrier, the metal catalyst was carried in the same manner as in Comparative Example 2, the final catalyst was named PtRu / CB-400.

Evaluation of Examples and Comparative Examples

(1) Measurement of Fluorine Incorporation Change in Carbon Black According to Fluorine Treatment Temperature

For the carbon blacks prepared from Comparative Example 1 and Examples 1 to 4, the amount of fluorine introduced and the content of carbon and oxygen were measured.

The amount of fluorine introduced and the contents of carbon and oxygen were measured using the energy dispersive X-ray spectroscopy (EDS) to measure the chemical composition and amount of the sample by detecting characteristic X-rays among various materials emitted by the accelerated electron beam in response to the specimen. It was.

The results are shown in the accompanying FIG. 1, which are summarized in Table 1 below.

division C content (% by weight) O content (% by weight) F content (% by weight) a CB-0 98.07 1.93 0 b CB-RT 85.51 1.26 13.23 c CB-100 82.74 1.07 16.19 d CB-300 80.05 0.97 18.98 e CB-400 73.11 0.94 25.95

1 and Table 1, from the conditions of Comparative Example 1 and Examples 1 to 4, when the fluorine gas treatment temperature is increased to 400 ° C. from room temperature at the surface of the carbon black, which is the catalyst carrier, the surface of the carbon black is increased. An increase in fluorine content could be observed. As a result, the highest fluorine content was shown when the fluorine gas treatment temperature was 400 ° C. That is, when the surface of the carbon black is to be treated using fluorine gas, it was confirmed that the degree of introduction of the fluorine functional group can be controlled by using the fluorine gas treatment temperature.

(2) Measurement of particle size and loading change of mixed metal supported on final metal catalyst according to fluorine treatment temperature

The particle size and loading level of the mixed metal supported on the metal catalysts prepared from Comparative Example 2 and Examples 5 to 8 were measured.

The particle size was measured using an X-ray diffractometer (Rigaky, model name: D / Max-III B) (see FIG. 2), and calculated using the Scherrer equation of Equation 1 below. Came out.

Where d is the average size of the particles, λ is the wavelength of X-ray radiation (0.154056 nm), θ is the angle of (220) peak, and B _2θ is the value in radians representing half the width of the diffraction peak.

In addition, the loading level of the mixed metal is released when the atoms excited at 6,000 to 8,000 K move to the ground state by introducing the sample solution into the Ar plasma formed by the high frequency induction coil using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The emission line and the emission intensity were measured to quantitatively analyze the elements of the mixed metal. The results are summarized in Table 2 below.

division Particle Average Size (nm) Pt loading level (%) Ru loading level (%) a PtRu / CB-0 4.84 4.74 1.1 b PtRu / CB-RT 3.98 7.05 2.81 c PtRu / CB-100 2.85 10.5 4.04 d PtRu / CB-300 2.53 10.6 3.75 e PtRu / CB-400 2.10 12.6 5.81

When looking at the metal catalysts prepared from Comparative Example 2 and Examples 5 to 8 through Table 2, the particle size of the mixed metal supported as the fluorine gas treatment temperature for the carbon black increases gradually from less than 4nm to about 2nm It can be seen that the loading level of the mixed metal is gradually increased. As a result, it was confirmed that the mixed metal is efficiently supported on the fluorinated carbon black compared to the carbon black which is not fluorinated, and the amount and particle size of the mixed metal supported on the carbon black can be controlled by using the fluorine treatment temperature.

(3) Measurement of the electrical activity of the metal catalyst

In order to measure the electrical activity of the metal catalysts prepared from Comparative Example 2 and Examples 5 to 8, voltage-current curves were prepared by cyclic voltammetry (CV). Nafion prepared metal catalyst powder A certain amount was attached to a glassy carbon electrode (GEC) and dried using a (Nafion ^® ) polymer, and a counter electrode used platinum foil, and Ag / AgCl was used as a reference electrode. In order to examine the electrochemical characteristics of the metal catalyst, cyclic voltammetry was measured in the range of 300 mV to 1100 mV using a 0.5 MH ₂ SO ₄ and 1.0 M CH ₃ OH mixed aqueous solution. The measurement results are shown in FIG. 3.

3, the metal catalyst prepared from the conditions of Comparative Example 2 and Examples 5 to 8 (a to e, respectively) has a larger and clearer methanol oxidation activity peak as the fluorine gas treatment temperature increases on the surface of the carbon black. It appears that the electrochemical activity was increased. This is interpreted that the mixed metal particles are efficiently carried without being aggregated evenly in the size of 2 to 4 nm. Thus, when the fluorinated carbon material was used as the catalyst carrier, the electrochemical activity was high, and the particle size and the loading ratio of the catalyst were most efficient when the fluorine treatment temperature was performed at 400 ° C.

Therefore, when a new fluorine functional group was introduced into the carbon black by the production method according to the present invention, the size of the catalyst was not only controlled, but the supporting efficiency of the mixed metal was increased, thereby increasing the activity of the final metal catalyst and improving the performance. .

1 is a view showing the results of analyzing the surface functional groups of the carbon black prepared according to Comparative Example 1 and Examples 1 to 4 of the present invention (a: CB-0, b: CB-RT, c: CB-100 , d: CB-300, e: CB-400)

2 is a view showing the results of X-ray diffraction analysis (XRD) of the metal catalyst prepared according to Comparative Example 2 and Examples 5 to 8 of the present invention. (a: PtRu / CB-0, b: PtRu / CB-RT, c: PtRu / CB-100, d: PtRu / CB-300, e: PtRu / CB-400)

Figure 3 is a diagram showing the electrochemical activity of the metal catalyst prepared according to Comparative Example 2 and Examples 5 to 8 of the present invention with a current-potential curve. (a: PtRu / CB-0, b: PtRu / CB-RT, c: PtRu / CB-100, d: PtRu / CB-300, e: PtRu / CB-400)

Claims (12)

(a) performing a fluorination treatment directly on the carbon-based support to prepare a carbon-based support having a fluorine functional group introduced therein; and (b) preparing a metal catalyst by supporting a metal on the carbon-based support obtained in step (a); The metal supported on the carbon-based support in step (b) is a mixed metal of Pt and Ru, the Pt content is 5 to 20% by weight based on the weight of the metal catalyst and the Ru content is 2 to 10% by weight Metal catalyst manufacturing method characterized in that. The method of claim 1, further comprising a pretreatment step for removing impurities present on the surface before step (a). The method of claim 1, wherein the fluorination treatment for the carbon-based support in the step (a) is carried out for 1 to 30 minutes under 0.01 to 1 MPa. The method of claim 1, wherein in the step (a) the fluorine treatment temperature for the carbon-based support is a metal catalyst manufacturing method, characterized in that more than room temperature 800 ℃. The method of claim 4, wherein the fluorine treatment temperature is at least 500 ° C. or less. The method according to claim 1, wherein the amount of fluorine introduced into the carbon-based support in step (a) is 5 to 40% by weight based on the weight of the carbon-based support. 7. The method of claim 6, wherein the amount of fluorine introduced is 10 to 30% by weight. The method of claim 1, wherein the particle size of the metal supported on the carbon-based support in the step (b) is 0.1 to 4.5nm metal catalyst manufacturing method. delete The method of claim 1, wherein the carbon-based support is selected from the group consisting of carbon black, activated carbon, carbon nanotubes, carbon fibers, graphite, graphite nanofibers, and mixtures thereof. A metal catalyst prepared by the method according to any one of claims 1 to 8 and 10. A fuel cell comprising the metal catalyst of claim 11.

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