KR100574030B1 - Electrocatalysts for fuel cell supported by porous carbon structure having regularly 3-dimensionally arranged spherical pores of uniform diameter and their preparation method - Google Patents

Abstract

The present invention relates to an electrode catalyst for a fuel cell, specifically 2 nm to 3 nm in a porous carbon structure in which spherical pores having a uniform diameter in the range of 5 nm to 1 μm are regularly arranged in three dimensions. Disclosed are an electrode catalyst for a fuel cell carrying an active metal of and a method for producing the same.

The electrocatalyst for a fuel cell according to the present invention can be prepared using a small amount of active metal, can disperse the metal into fine sizes of 2 to 3 nm, and the movement and diffusion of reactants and products between regularly arranged pores It is smooth and has higher catalytic activity than Pt-Ru or Pt catalyst prepared using a conventional carbon black as a support, thereby improving the performance of the fuel cell, and can be prepared by a simple method in aqueous solution.

Porous Carbon Supports, Fuel Cells, Electrode Catalysts

Description

Electrocatalysts for fuel cell supported by porous carbon structure having regularly 3-dimensionally arranged spherical pores of uniform diameter and their preparation method             

Figure 1 schematically shows a synthetic procedure for producing a porous carbon structure used as a support for the electrode catalyst for a novel fuel cell of the present invention.

FIG. 2 is a scanning electron microscope (SEM) photograph of a porous carbon structure prepared according to the synthesis procedure shown in FIG. 1.

3 is a Brunauer-Emmett-Teller (BET) adsorption isotherm of a platinum-ruthenium alloy catalyst for fuel cells supported by a porous carbon structure synthesized according to the present invention.

Figure 4 shows the X-ray diffraction analysis pattern of the platinum-ruthenium alloy catalyst and commercial platinum-ruthenium alloy catalyst (E-TEK) supported by the porous carbon structure synthesized according to the present invention.

5 is a transmission electron micrograph (TEM) of a commercial platinum-ruthenium alloy catalyst (E-TEK) and the platinum-ruthenium alloy catalyst of the present invention. In the photograph of FIG. 5, a is a commercial platinum-ruthenium alloy catalyst (E-TEK), and small black spheres are platinum-ruthenium alloy particles. b shows a platinum-ruthenium alloy catalyst using a porous carbon structure having pores having a diameter of 68 nm, c at 245 nm and d at 512 nm.

Figure 6a is a platinum-ruthenium alloy catalyst prepared by using a porous carbon structure having pores 25 nm and 68 nm in diameter according to the present invention, commercial carbon black (Vulcan XC-72, Cabot Co.) as a support It is a cyclic voltammogram showing the activity of the platinum-ruthenium alloy catalyst prepared using the catalyst and the methanol oxidation reaction of a commercial platinum-ruthenium alloy catalyst (E-TEK). 6B is a ethanol oxidation reaction of a platinum-ruthenium alloy catalyst and a commercial platinum-ruthenium alloy catalyst (E-TEK) prepared using a porous carbon structure having a pore diameter of 25 nm as a support according to the present invention. Cyclic voltammogram showing the activity of the catalyst.

7A and 7B illustrate a platinum-ruthenium alloy catalyst supported on a porous carbon structure having different pore sizes and a platinum-ruthenium alloy catalyst supported on commercial carbon black (Vulcan XC-72, Cabot Co.) according to the present invention. Unit cell performance curves measured at 30 ° C (7a) and 70 ° C (7b) of commercial platinum-ruthenium alloy catalysts (E-TEK). 7C and 7D illustrate 30 ° C (7c) of a platinum-ruthenium-cobalt-tungsten alloy catalyst and a commercial platinum-ruthenium alloy catalyst (E-TEK) supported on a porous carbon structure having a pore size of 250 nm according to the present invention. ) And unit cell performance curves measured at 70 ° C (7d).

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode catalyst for a fuel cell in which spherical pores having a uniform diameter are supported by three-dimensionally arranged porous carbon structures, and a method of manufacturing the same. More specifically, in order to increase the activity of a fuel cell, a porous carbon structure (ordinary carbon) in which spherical pores having excellent electrical conductivity and a uniform diameter are regularly arranged in three dimensions is used as a support of an active metal. An electrode catalyst for a fuel cell and a method of manufacturing the same.

Fuel cell is a device that directly converts chemical energy of fuel into electric and thermal energy by electrochemical reaction. It is a clean power generation technology with high efficiency and no environmental problems since there is no combustion process or driving device. Since the space program has been developed in the United States as a power source for spacecraft, research is being actively conducted around the world for various applications such as power generation, household, transportation, and mobile power. Depending on the operating temperature and the type of electrolyte used, the fuel cell has a phosphate type (PAFC: Phosphoric Acid Fuel Cell), a molten carbonate type (MCFC: Molten Carbonate Fuel Cell), a solid oxide type (SOFC), and an alkaline type. (Alkaline Fuel Cell) and Polymer Electrolyte (PEMFC) Proton Exchange Membrane Fuel Cell (PEMFC), and have different power generation characteristics depending on reaction temperature and structure. Among these, the polymer electrolyte fuel cell is classified into a hydrogen fuel cell and a methanol fuel cell according to the type of fuel used. In particular, the Direct Methanol Fuel Cell (DMFC), which uses methanol directly as a fuel without a reformer, can operate at a relatively low temperature because the fuel is supplied directly to the anode (cathode) in the liquid phase, and the device can be miniaturized. It is a power generation system that is attracting attention as the next generation alternative energy such as a small portable power source or an automobile because of its advantages.

In a direct methanol fuel cell (DMFC), methanol is oxidized at the anode (cathode) and oxygen is supplied to air and reduced at the cathode (anode) as shown below.

Cathode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ^- E _o = -0.015 V vs NHE

^{_{Cathode: O 2 + 4H + + 4e}} - → 2H 2 OE o = + 1.229V vs NHE

Total reaction: 2CH ₃ OH + 3O ₂ → 2CO ₂ + 4H ₂ OE _o = + 1.24V vs NHE

The key factors that determine the efficiency of a fuel cell are the oxidation and reduction electrodes used as catalysts. The Pt ₅₀ Ru ₅₀ alloy catalyst, in which ruthenium is alloyed with platinum in a molar ratio of 1: 1, is most commonly used as an anode (fuel electrode), and platinum is commonly used as a cathode (air electrode). Currently, electrode catalysts used for the oxidation and reduction of fuel and air in direct methanol fuel cells (DMFCs) have fine particles of active metal catalysts on carbon black (eg, Vulcan XC-72, Cabot Co.) supports with excellent electrical conductivity. It is prepared by dispersing in the form. In connection with the improvement of the activity of the fuel cell, there are several characteristics required for Pt-Ru / C and Pt / C, which are the material of the catalyst layer.

First, the size of the dispersed catalyst metal particles should be small and should be uniformly dispersed on the support to provide a wide range of catalytic activity points and thus have a large surface area for oxidation and reduction reactions.

Second, the carbon used as the support should have a porous structure to facilitate the movement of the reactants and products of the gas phase and liquid phase redox reactions.

Third, the catalyst metal particles should be strongly supported so that the catalyst metal particles cannot be separated from the support by physical and chemical impacts.

As such, the support used in electrode production of fuel cells is required to have a suitable porosity, excellent electrical conductivity and a large surface area. In particular, in the fuel electrode of the direct methanol fuel cell, a mixture of methanol and water passes through the electrode catalyst support to cause methanol oxidation in the catalyst layer. Therefore, the electrode catalyst support must have excellent electrical conductivity and hydrophilicity, and fuel and gas can move freely. It must be a material with a uniform diameter and well developed internal pores in three dimensions.

The inventors of the present invention disclose a method for producing porous carbon molecular sieves having a uniform size and regularity using a liquid carbon precursor, which is a method for producing porous carbon having excellent electrical conductivity and having uniform pores and a large surface area. It is already filed in 57082. That is, in the prior application, a silica colloidal crystal mold is made, a liquid carbon precursor (carbohydrate, a polymer monomer and an initiator) is injected between the periphery and the inner gap of the mold, then polymerized and molded, and carbonized under an inert gas atmosphere. After the process, a method of preparing a porous carbon sieve by removing the silica template with hydrogen fluoride was proposed. The carbon molecular sieve prepared in this way is composed of carbon, which is characterized by the microstructure of the porous carbon, that is, a form in which the pores are regularly formed in the carbon solid, and the surface template porous carbon. Structural control is possible to form regularly, and all of these carbons have three-dimensionally connected pore structures, and are excellent in electrical conductivity because carbon hexagon rings are combined such as graphite.

The present inventors fabricated an electrode catalyst using a porous carbon structure having excellent electrical conductivity and regular diameters of three-dimensionally arranged spherical pores as a support when preparing an electrode catalyst. The present invention has been found to be useful as an electrode catalyst for methanol fuel cells.

That is, a first object of the present invention is to provide an electrode catalyst for a fuel cell supported by a porous carbon structure in which spherical pores having a uniform diameter are regularly arranged in three dimensions.

It is also a second object of the present invention to provide a method for preparing the electrode catalyst.

According to the first object of the present invention, an electrode catalyst for a fuel cell supported by a porous carbon structure in which spherical pores having a uniform diameter are arranged in three dimensions regularly is a spherical pore having a uniform diameter in the range of 5 nm to 1 μm in diameter. In this three-dimensionally arranged porous carbon structure, an active metal having a size of 2 nm to 3 nm is supported.

Electrode catalyst for fuel cells of the present invention is a direct methanol fuel cell (DMFC), direct ethanol fuel cell (DEFC: direct ethanol fuel cell) such as direct liquid alcohol It can be applied not only to a fuel cell used as fuel but also to an anode (fuel electrode) of a hydrogen fuel cell.

An electrode catalyst for a fuel cell prepared by using a porous carbon structure in which spherical pores having a uniform diameter of the present invention are regularly arranged in three dimensions as a support has the following advantages.

First, since the porous carbon structure used in the present invention has a surface area of about 2-4 times larger than that of carbon black, an electrode catalyst may be prepared using a smaller amount of carbon than carbon black. In other words, because of the large surface area, the space for supporting the metal catalyst particles increases, so that a large amount of the metal catalyst particles can be supported even with a small amount, and the particle size is small (2- 3 nm) metal catalysts are possible.

Secondly, the pores are arranged in three-dimensionally well in the porous carbon structure to facilitate the movement and diffusion of fuel, air (oxygen) and reaction products so that the reaction proceeds quickly and the reaction products can be easily discharged.

The porous carbon structure used as a support in an electrode catalyst for a fuel cell according to the first object of the present invention can be prepared according to the method described in Korean Patent Application No. 2000-57082, the contents of which are incorporated herein by reference. . Specifically, as shown in FIG. 1, spherical silica having a diameter in the range of 5 nm to 1 μm is used by sedimentation, centrifugation, filtration, or compression. To form a silica colloidal crystal template, and to the pores between the spherical silicas forming the template, a hydrocarbon precursor such as a liquid or gaseous phase, for example, a carbohydrate, or various polymer monomers and an initiator, and a polymerization catalyst, if necessary. After injection, when the polymer monomer, the initiator and the catalyst are injected, the polymer is polymerized through the usual polymerization reaction according to the type of polymer monomer, and then the obtained silica-polymer or other carbon precursor complex is inert gas (for example, argon or Nitrogen gas) to carbonize at about 800 to 1000 ° C. under an atmosphere to obtain a carbon-silica template composite. To obtain a porous carbon structure by removing only the dissolved mold. At this time, by controlling the size of the silica used, the size of the carbon molecular sieve can be freely selected in the range of 5 nm to 1 μm to adjust the size of the pores, and the size of the pores is uniform by adjusting the size of the spherical silica uniformly. The silica colloidal crystal mold prepared by laminating uniformly sized spherical silica is arranged in a regular manner. Since the spherical silica is regularly arranged, the porous carbon structure used as a support for the electrode catalyst of the present invention is characterized in that Have

In addition, the carbon structure is divinylbenzene (DVB), acrylonitrile (acrylonitrile), phenolic resin (phenolic resin), vinyl chloride, vinyl acetate, styrene, methacrylate, methyl methacrylate, ethylene glycol dimethacrylate, Furfuryl alcohol, resorcinol-formaldehyde (RF), sugar, a compound represented by the general formula CH ₂ = CRR 'wherein R and R' are alkyl or aryl groups or mesophase pitch ( It is prepared using a carbon precursor which forms graphitic carbon by a carbonation reaction selected from mesophase pitch.

Table 1 below shows the characteristics of the porous carbon structures having various sizes of pores prepared for use as the support of the electrode catalyst of the present invention together with the properties of the carbon black used as the conventional electrode support. The surface area of the porous carbon was measured by the Brunauer-Emmet-Teller (BET) method, and the pore volume was measured by the BJH method. BET absorbs nitrogen gas while applying pressure to the sample at 77 K, and desorbs the adsorbed nitrogen gas while depressurizing it to atmospheric pressure to measure the surface area and pore volume of the sample.

  Carbon support BET surface area (m ² / g) Micropore Area (m ² / g) Meso / macropore area (m ² / g) Total pore volume (cc / g) Micropore volume (cc / g) Carbon black (Vulcan XC-72) 232 87 145 0.32 0.04 Porous Carbon (25nm) 845 195 650 3.66 0.07 Porous Carbon (68nm) 691 483 218 1.63 0.12 Porous Carbon (245nm) 605 400 205 0.81 0.13 Porous Carbon (512nm) 509 313 196 0.75 0.16 Porous Carbon (806 nm) 449 267 182 0.71 0.15

In the platinum-ruthenium / carbon electrode of the present invention prepared by using a porous carbon structure having uniformly arranged uniform pores as a support, the amount of porous carbon is 20 wt% (total metal weight: 80 wt%) of the total catalyst weight. Even if the catalyst is prepared by reducing the amount (about 50% less than carbon black), the catalyst having higher activity than the Pt-Ru (molar ratio 1: 1) catalyst (E-TEK, supported by metal at 60wt.%), Which is currently available, is available. It can manufacture.

The active metal supported on the electrode catalyst for a fuel cell according to the first object of the present invention may be any metal having an activity in the oxidation reaction of the fuel of the fuel cell, for example, platinum (Pt), ruthenium (Ru), Selected from the group consisting of rhodium (Rh), molybdenum (Mo), osmium (Os), iridium (Ir), rhenium (Re), palladium (Pd), vanadium (V), cobalt (Co) and tungsten (W) It contains more than one kind of metal. For example, known catalytic metals such as monocomponent systems such as platinum (Pt) or bicomponent systems such as platinum-ruthenium (Pt-Ru) alloys, as well as three-component systems such as Pt-Ru-Rh alloys, four-component systems, For example, it may include a Pt-Ru-Co-W alloy or a Pt-Ru-Mo-W alloy and other multicomponent catalyst metals. These metals may be loaded in amounts of at least 5% of the total weight of the catalyst, as much as at least 80% by weight, preferably from 5% to 95% by weight. In other words, the electrode catalyst for a fuel cell of the present invention may carry a metal corresponding to about four times or more the weight of the carbon support. This is because the carbon support used in the electrode catalyst for fuel cell of the present invention has a surface area of about 2 to 4 times per unit mass compared to the conventional carbon black support, so that the surface area on which the metal catalyst particles can be supported is widened to equal the weight. Compared to carbon black of the present invention, not only can support a larger amount of metal catalyst particles, but also metals can be supported on a support with a very small size of 2 to 3 nm in diameter, so that expensive precious metals can be efficiently used. Is also advantageous. For example, a platinum-ruthenium / carbon electrode for a fuel cell supported by a porous carbon structure in which spherical pores having a uniform diameter are arranged in three dimensions regularly according to the present invention may be used in the total catalyst weight. Even if the catalyst is prepared by reducing it to 20 wt% or less (about 50% less than carbon black), Pt-Ru (mole ratio 1: 1) catalyst (E-TEK, 60 wt.%), Which is a commercially available electrode catalyst, Catalyst having better activity than metal supported).

On the other hand, in general, in the preparation of the electrode catalyst, the smaller the supporting ratio of the catalyst metal to the support, the higher the amount of support to be used to support the same amount of the catalyst metal, so that it is used to obtain the same amount of the active catalyst. The amount of support to be increased also. In this case, in preparing the electrode of the fuel cell, a large amount of catalyst must be applied thickly to the carbon sheet, which causes cracking during drying or during use, thereby degrading the performance of the fuel cell. However, the catalyst system of the present invention has a higher metal loading ratio compared to the catalyst system using a conventional carbon black as a support, for example, compared with the 60% loading ratio of a commercially available E-TEK catalyst. When the catalyst of has 80% of the metal loading amount, since the amount of the support used to support the same amount of metal is only 1/2, since a small amount of catalyst is used entirely, the above cracking phenomenon can be prevented. have. In addition, the particle size of the catalyst supported by the wide surface area of the porous carbon support of the present invention is also reduced, and the metal particles can be dispersed to about 2 to 3 nm. Of course, it is possible to support the amount of the catalyst metal as much as 5% of the total weight of the catalyst. As a result, the relative weight of the metal can be widely chosen depending on the intended use.

In addition, the regular and three-dimensional well-developed uniform pores of the porous carbon structure used as the metal support of the electrode catalyst for fuel cells of the present invention frees the movement and diffusion of the fuel so that the fuel easily reaches the catalyst surface and reacts. This has the advantage that it proceeds quickly and the reaction products can be easily discharged.

According to a second aspect of the present invention, a method of preparing an electrode catalyst for a fuel cell may include the following steps: a) dissolving a water-soluble salt of a metal having catalytic activity in water; b) injecting an aqueous slurry of a carbon structure with uniformly arranged uniform pores into a reaction vessel and mixing with an aqueous solution of a water-soluble metal salt; c) adjusting the pH of the reaction solution to 8-9 by adding a basic or acidic aqueous solution; d) adding a reducing agent to the reaction solution to form a precipitate; And f) recovering the catalyst.

The method for preparing an electrode catalyst of a fuel cell according to the present invention has a large surface area of metal catalyst particles which are reduced by slowly adding a dispersion solution of a carbon structure and a reducing agent to a solution of a metal salt under stirring at a room temperature in a relatively simple manner without a complicated process. It is not only uniformly dispersed on the porous spherical carbon capsule support having a large pore volume, but also makes it possible to prepare metal catalyst particles of extremely fine size (2 to 3 nm).

In step a) of the method of preparing the electrode catalyst of the fuel cell according to the second object of the present invention, the water-soluble salt of the catalyzed metal may be an acidic or basic salt. Examples of the water-soluble metal salt include H ₂ PtCl ₆ , PtCl ₂ , PtCl ₄ , and (NH ₄ ) ₂ PtCl _{4 for} platinum, RuCl _{3 for} ruthenium, Na ₂ WO ₄ , and molybdenum for tungsten. Na ₂ MoO ₄ , K ₂ IrCl _{6 for} iridium, CoCl _{2 for} cobalt, OsCl _{3 for} osmium, NiCl ₂ , Ni (ClO ₄ ) ₂ , NiSO ₄ , and the like. The amount of these metal salts to be used can be determined stoichiometrically according to the amount of metal to be supported on the catalyst support to be prepared. For example, when using a Pt-Ru alloy, the use ratio can also be determined by stoichiometric calculation. have. The concentration at which the water-soluble metal salt is dissolved in water may be determined according to the number of moles of the metal salt to be used. The step of preparing the aqueous solution may vary depending on the solubility and concentration of each metal salt, the dissolution temperature, etc., but it is usually sufficient to stir for about 20 minutes to 1 hour.

In step b) of the method according to the second object of the present invention, the porous carbon structure, i.e. the slurry in the support of a spherical pore having a uniform diameter, three-dimensionally arranged, for example, 100 ml of water It is prepared by adding a support to water at an appropriate amount of carbon support ratio and stirring. At this time, the support aggregate may be separated into respective support particles, and sonication may be performed in the middle of stirring to degas the air in the pores of the support. The slurry is prepared in a separate vessel and mixed with the aqueous metal salt solution in the reaction vessel. The concentration of the water-soluble metal salt in the carbon support slurry in the aqueous solution of the water-soluble metal salt is in the range of about 1 to 3 mM, preferably with respect to the total amount of water included in the metal salt solution, water included in the support slurry, and water introduced by other sources. It is preferable to dilute by adding water to about 2 mM. Diluting the aqueous solution of the metal salt is previously diluted to an appropriate concentration in order to prevent the metal particles from growing by agglomeration and agglomeration of the respective particles when the catalyst metal is precipitated by the reduction reaction in the following steps. The stirring time is suitably about 1 to 2 hours.

Step c) of the method according to the second object of the present invention is a step of adjusting to an appropriate pH range in advance so that a smooth reduction reaction may proceed in the following reduction reaction step. Conventional acid or base aqueous solution may be used for pH adjustment.

Step d) of the method according to the second object of the present invention is a step of reducing the catalyst metal in the water-soluble salt state to precipitate it on the surface of the support as a metal. As a reducing agent, an aqueous NaBH ₄ , LiBH ₄ or AlBH ₄ solution, preferably an aqueous NaBH ₄ solution, generates an excess of H ⁻ , corresponding to about 10 times the number of moles of metal, relative to the number of moles of metal to be reduced. Use an aqueous NaBH ₄ solution in excess.

Step e) of the method according to the second object of the present invention is a process of separating and recovering a catalyst produced by precipitation of metal particles on the surface of the support by the reduction reaction in step d). The catalyst particles are then precipitated, the supernatant is separated off and the precipitate is washed repeatedly with water and dried. The washing process is a process for removing impurities such as chlorine contained in the water-soluble metal salt.

The above steps are carried out under an air atmosphere at room temperature and atmospheric pressure unless otherwise noted, and distilled or deionized water is preferably used for the water used.

Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited by these Examples.

Example

A method for producing a porous carbon structure in which spherical pores having a uniform diameter are regularly arranged is described in detail in Korean Patent Application No. 10-2000-57082, which is incorporated herein by reference, and the preparation thereof is incorporated herein by reference. This is briefly explained.

Preparation Example 1

Preparation of Spherical Silica of 100 nm or Less

1500 ml of cyclohexane, 60 ml of n-hexanol and 190 ml of Tergitol NP-9 (nonionic surfactant) were added to a 1 L round bottom flask, followed by stirring sufficiently to form a reverse micelle of constant size. Then, 60 ml of water and 28% 17 ml of ammonia water is added and stirred for about 30 minutes to obtain a microemulsion state.

100 ml of TEOS (tetraethyl orthosilicate) was added to the solution, and the solution was continuously stirred for about 3 to 4 days. The solution turned white and colloidal silica was formed. After removal of the cyclohexane solvent using a rotary vacuum evaporator, around 1 hour after adding ethanol (absolute) to disperse the surfactants forming the reverse micelles around the colloidal silica to be dispersed in the ethanol solution Stir to a degree.

The colloidal silica ethanol solution is centrifuged at 5000 to 6000 rpm for 1 to 2 hours using a centrifuge to separate the colloidal silica from the ethanol solution. The colloidal silica was washed with an ethanol solution and centrifuged two to three times to remove residual surfactant and dried in an oven at 70 to 80 ° C. to obtain spherical silica having a diameter of less than 100 nm.

In the above method, the size of the spherical silica can be adjusted by adjusting the amount of the surfactant, water, and TEOS. In the present invention, spherical silica having diameters of 25 nm and 68 nm, as listed in Table 1, was prepared.

Preparation Example 2.

Preparation of Spherical Silica Over 100nm

1000 ml of ethanol (absolute), 40 ml of 28wt% ammonia and 40 ml of distilled water were added to a 1L round bottom flask, and the mixture was stirred and mixed well. Then, 60 ml of TEOS was added and the silicon alkoxide ions in the solution were sufficiently hydrolyzed. Stir for about 6-7 hours to grow to a size.

Similar to Preparation Example 1, the silica ethanol suspension was centrifuged at about 3000 rpm for 20 to 30 minutes to remove the ethanol solution from the colloidal silica, followed by washing the colloidal silica with distilled water and centrifuging 2-3 times. After drying in the oven at 70 ~ 80 ℃ to obtain spherical silica about 400 nm.

Spherical silica having a diameter of 100 nm or more listed in Table 1 was prepared by adjusting the mixing ratio of ammonia, water and TEOS.

Preparation Example 3.

Fabrication of Porous Carbon Structures

A porous carbon structure can be obtained by filling a hollow void between the spherical silicas of a silica mold made by stacking spherical silicas with a hydrocarbon or polymer monomer such as a saccharide as a carbon precursor and then carbonizing the polymerized polymer. The following structure was synthesized.

First, 1 g of spherical silica having a uniform size of about 250 nm in diameter is laminated well using sedimentation method to form a silica mold, and then mixed with 4 ml of divinylbenzene monomer at a ratio of 0.1845 g of AIBN (initiator). After immersing the mold in one solution to inject DVB and AIBN into the pores, radical polymerization was carried out at about 70 ° C. for 12 hours, and then argon gas was flowed from a tube furnace for 8 hours at about 1000 ° C. After the carbonization reaction, the porous carbon structure was synthesized by removing the silica template using a hydrogen fluoride solution.

Secondly, a solution of a mixture of 5g of phenol and 3.5 ml of formaldehyde and 0.28ml of sulfuric acid catalyst was injected into the pores of the silica mold prepared in the same manner as above, and condensation reaction was carried out at 125 ° C. to form a phenolic resin. After the composite was prepared, a carbonaceous reaction was carried out at about 1000 ° C. for 8 hours while argon gas was flowed from a tube furnace, and then a porous carbon structure was synthesized by removing the silica template using a hydrogen fluoride solution. In this case, it is possible to manufacture a porous carbon structure having two different forms through morphology control. First, a porous carbon structure in which pores between spherical silica particles are filled by filling the empty voids between the stacked spherical silicas with phenol resin and then undergoing a polymerization reaction and a carbonization reaction and then removing the silica template. There is a method (volume templating). In the second method, AlCl ₃ is used to displace Al on the surfaces of spherical silicas, and the acid generated by Al causes the condensation reaction of phenol and formaldehyde to proceed regularly only on the silica surface. There is a method of manufacturing a porous carbon structure in which a carbon shell is formed only on a silica surface by removing a silica mold using a hydrogen solution.

A scanning electron microscope (SEM) photograph of the porous carbon structure having pores having various diameters prepared in Preparation Example 3 is shown in FIG. 2. Specifically, SEM images of porous carbon structures each having a diameter of a) about 25 nm, b) about 68 nm, c) about 245 nm, and d) about 512 nm.

In addition, the surface area and other properties of each of the carbon structures are shown in Table 1 together with the properties of other supports.

Example 1

Preparation of Pt-Ru Catalyst

1 g and 0.5206 g of H ₂ PtCl ₆ and RuCl ₃ were added to a 250 ml beaker containing 80 ml of distilled water in a 1: 1 molar ratio, and stirred for 30 minutes to dissolve and prepare a metal salt solution. Transfer the solution. Into a 250 ml beaker containing 100 ml of distilled water was added 0.1552 g of the porous carbon structure prepared by the volume template method, which had pores of 245 nm in diameter, stirred for 30 minutes, and then slowly added to the metal salt solution. After addition, 1800 ml of distilled water was added thereto, and the total concentration of the metal salt was diluted to about 2 mM, followed by stirring for 1 hour. Then, pH was adjusted to 8 by adding 20 wt% NaOH aqueous solution, and then 1.5 g of NaBH ₄ was dissolved in 20 ml of distilled water, slowly added to the metal salt-carbon mixed dispersion, stirred for about 2 hours, and then the stirring was stopped. It was left to form a precipitate. When the supernatant solution is clear, the supernatant is discarded, filtered using 0.2 μm nylon filter paper, washed three times with distilled water and dried at 80 ° C. in a porous carbon structure having uniform pore diameters of 245 nm. 0.76 g of an electrode catalyst for a fuel cell carrying 80 wt% of a Pt-Ru alloy catalyst metal having a: 1 molar ratio was obtained.

Examples 2-5

25 nm (Example 2) and 68 nm (Example 3) regularly arranged in the same manner as in Example 1, except that porous carbon structures having pores having diameters of 25, 68, 512 and 806 nm were used. 0.74 to 0.76 g of an electrode catalyst for a fuel cell in which a Pt-Ru alloy catalyst metal having a 1: 1 molar ratio of 80 wt% is supported on a porous carbon structure having uniform pores of 512 nm (Example 4) and 812 nm (Example 5). Got.

TEM images of the pore sizes of the porous carbon support in the catalysts prepared in Examples 1 to 5 are 68, 245 and 512 nm are shown in FIGS. 5A, 5B, and 5C, respectively.

Example 6

Preparation of PtRuCoW Four-Component Catalysts

250㎖ the beaker containing distilled water at _{150㎖ H 2 PtCl 6, RuCl 3} , CoCl 2, the _{Na 2 WO 4 Pt: Ru:} Co: the molar ratio of W 0.55: 0.22: 0.11: 0.11 H 2 PtCl 6 to the 2.7869g, 0.5462g of RuCl _3, 0.1428g of CoCl _{2 and} 0.3628g of Na ₂ WO ₄ were added thereto, stirred for 30 minutes to dissolve, and then, the metal salt solution was transferred to a 5L Erlenmeyer flask. 0.3906 g of porous carbon having a pore diameter of 250 nm (20 wt% of metal weight) was mixed with 100 ml of distilled water in a 250 ml beaker, stirred for 30 minutes, and slowly added to the metal salt solution. The total concentration of the metal salt was about 2 mM. 4.5 L of distilled water was added and diluted, followed by stirring for about 1 hour. After adjusting the pH to 8-9 using 20wt% NaOH solution, 3.8g NaBH ₄ dissolved in 40ml of distilled water was slowly added to the metal salt-carbon mixed solution and stirred for about 2 hours, and then the stirring was stopped and left to stand. A precipitate formed. When the upper solution was clear, the filter was filtered using a nylon filter paper having a pore of 0.2 μm, washed three times with distilled water, and dried at 80 ° C. to prepare a catalyst having a PtRuCoW 4-component alloy.

Comparative Example 1

Using 0.4137 g of Vulcan XC-72 carbon black from Cabot Co. as the carbon support, the same method as in Example 1 was repeated to carry a 60 wt% Pt-Ru alloy catalyst metal having a 1: 1 molar ratio on the carbon black. 0.98 g of battery electrode catalysts were obtained.

Experimental Example 1

Adsorption experiments were carried out on the catalysts using carbon structures having pore sizes of 25 nm and 68 nm in the catalysts prepared in Examples as a support.

0.1 g of the catalyst was weighed and placed in a sample analysis tube and pretreated at 150 ° C. for 4 hours to remove moisture and impurities adsorbed on the sample. Then, nitrogen gas was adsorbed onto the sample while increasing the relative pressure from 0 to 1 under liquid nitrogen. While depressurizing the pressure from 1 to 0.1, the adsorption volume according to the relative pressure was measured while desorbing the nitrogen gas adsorbed on the sample, and the results are shown as adsorption isotherms in FIG. In this case, the surface area, pore volume, and pore size distribution of the sample may be measured using the BET equation and the BJH method using the volume of the adsorbed nitrogen gas molecules. The BET adsorption isotherm of the porous carbon structures and catalysts prepared in the present invention shows the characteristics of the mesoporous material corresponding to Type VI according to the definition of IUPAC, and the surface area and pore volume are shown in Table 1.

The X-ray diffraction (XRD) analysis pattern of the Pt-Ru catalyst prepared in Examples is shown in FIG. 4. X-ray diffraction analysis using Rigaku 1200, Cu Kα irradiation, Ni-β filter, 2θ value range of 10 ^{o to} 100 ^o at 40 kV, 20 mA at 4 ^o / min. Analyze The crystal structure on the XRD shows the face-centered cubic (fcc) structure of platinum. The XRD pattern of each catalyst synthesized by NaBH ₄ reduction method using porous carbon and Vulcan carbon as a support shows the same pattern as E-TEK catalyst at around 2θ = 40, 68 and 83. It can be seen that this is well done, the particle size of each catalyst was calculated through the peak broadening of the (220) diffraction of the platinum fcc lattice using the Scherrer's equation. The approximate particle size of each catalyst was about 2 to 3 nm, which is in agreement with the results confirmed by electron micrographs.

In addition, the state of the Pt-Ru catalyst supported on the carbon support in the Pt-Ru electrode catalyst prepared in Examples was observed by electron microscopy and the photo is shown in FIG. 5.

Experimental Example 2

Evaluation of Catalytic Activity for Methanol Oxidation

The catalytic activity of methanol oxidation of Pt-Ru alloy catalyst prepared using porous carbon having different size pores of the present invention as a support was measured by cyclic voltammetry (CV). . The result was synthesized using a commercially available E-TEK Pt-Ru alloy catalyst (supporting 60 wt.% Metal) and carbon black (Vulcan XC-72, Cabot Co.) prepared in Preparation Example 1 as a support. (Molar ratio 1: 1) It is shown in FIG. 6A compared with the activity of an alloy catalyst.

On the other hand, Figure 6b is a ethanol oxidation reaction of the platinum-ruthenium alloy catalyst and commercial platinum-ruthenium alloy catalyst (E-TEK) prepared using a porous carbon having a pore diameter of 25nm synthesized according to the present invention as a support Cyclic voltammogram showing the activity of the catalyst.

The cyclic voltammogram used EG & G Model 362 Scanning Potentiostat and the reaction cell was made of Teflon. The reference electrode was placed very close to the working electrode using a labyrinth of silver / silver chloride (Ag / AgCl) electrodes using luggin capillary. The counter electrode (Pt gauze, 100 mesh, Aldrich) of a larger area than the working electrode was used. The electrolyte used was an aqueous solution mixed with 0.5M sulfuric acid solution and 1.0M methanol solution, and was used after sufficiently purging nitrogen gas in the solution to remove dissolved oxygen in the solution. The working electrode was placed between the cells after applying carbon catalyst (1.5 cm x 1.5 cm) and a thin piece of gold was sandwiched between the rubber gasket and the carbon paper to fix the cross section of the working electrode exposed to the electrolyte. Was about 0.95 cm 2. The potential was varied at a scan rate of 20 mV / s in the range from -350 mV to 1350 mV.

In FIG. 6A, each electrode catalyst exhibits an oxidation current peak in a 0.25 to 1 V region (vs. Ag / AgCl) and a reduction current peak in a 0.4 to 0.6 V region (vs. Ag / AgCl). As shown in the figure, this was prepared by using a porous carbon structure to support Pt ₅₀ Ru of the invention ₅₀ the catalyst is Pt ₅₀ Ru ₅₀ catalyst was prepared by using Vulcan carbon as a support (Example 1) or E-TEK catalyst It can be seen that it shows more improved catalytic activity for methanol oxidation. This is considered to be due to some properties of the porous carbon of the present invention. That is, the metal catalyst is uniformly dispersed over a large surface area to provide a wide reaction area for methanol oxidation, and the uniform and well-developed uniform pores freely move and diffuse the electrolyte solution, allowing methanol to be a fuel. It is considered that it showed superior activity compared to the conventional carbon black support because the methanol oxidation reaction can proceed quickly with easy access to the catalyst surface.

In Figure 6b, it can be seen that the catalyst of the present invention has superior activity compared to commercially available catalysts for the oxidation reaction of ethanol as well as methanol.

Experimental Example 3

Unit battery performance test

The anode is equipped with an electrode prepared by using the catalysts prepared in Examples 1 to 6 and Preparation Example 1 or commercial E-TEK catalyst electrode, and the cathode is equipped with Pt black (Johnson Matthey), respectively. Phosphorus unit cell was fabricated, Nafion was used as electrolyte, 2M methanol solution was flowed to the anode at 1ml / min, and oxygen gas was flowed at 300ml / min to the cathode, resulting in current density and battery The unit cell performance test was performed by measuring the voltage, and the results were obtained using a commercially available E-TEK Pt-Ru alloy catalyst (supporting 60 wt.% Metal) and carbon black prepared in Preparation Example 1 (Vulcan XC-72, Cabot Co. 7 shows the results of the unit cell performance test of the Pt-Ru (molar ratio 1: 1) alloy catalyst synthesized using the same as the support.

7A and 7B, it can be seen that the unit cell performance for methanol oxidation of the Pt-Ru alloy catalyst prepared using the porous carbon structure of the present invention as a support was improved by 15% or more compared to the E-TEK catalyst. It can be seen that the electrode catalyst of the invention is a very good catalyst for fuel cells.

7C is a unit measured at 30 ° C. (7a) and 70 ° C. (7b) of a commercially available platinum-ruthenium alloy catalyst (E-TEK) and a catalyst carrying a PtRuCoW tetracomponent alloy on porous carbon with pores having a diameter of about 245 nm. Cell performance curve. The platinum-ruthenium alloy catalyst supported on the porous carbon with diameter of 245nm showed methanol oxidation performance improved by about 30% over the commercial platinum-ruthenium alloy catalyst at 30 ° C, whereas the PtRuCoW four-component alloy catalyst had about 60% performance. At 70 ° C, methanol oxidation was improved by about 15% over the commercial platinum-ruthenium alloy catalyst supported on porous carbon of 250 nm in diameter, whereas the platinum-ruthenium-cobalt-tungsten tetracomponent alloy catalyst was about 70%. 27% performance improvement.

As described above, according to the present invention, an electrocatalyst for a fuel cell manufactured using a porous carbon structure having excellent electrical conductivity, a large surface area, and a uniform diameter of three-dimensionally arranged porous carbon structures as a support is It can be prepared using a small amount of active metal, can disperse the metal into fine size of 2 to 3 nm, and smoothly transfer and diffusion of reactants and products through regularly arranged pores, so that the conventional carbon black is used as a support. It has a higher catalytic activity than the Pt-Ru or Pt catalyst prepared by the present invention can improve the performance of the fuel cell, it can be prepared by a simple method in the aqueous solution state.

Claims (6)

In a porous carbon structure in which spherical pores having a uniform diameter in the range of 5 nm to 1 μm in diameter are arranged in three dimensions regularly, an active metal having a size of 2 nm to 3 nm is supported at 5 to 95% by weight based on the total catalyst weight. An electrode catalyst for fuel cell, characterized in that. The method of claim 1, wherein the carbon structure is divinylbenzene, acrylonitrile, phenol resin, vinyl chloride, vinyl acetate, styrene, methacrylate, methyl methacrylate, ethylene glycol dimethacrylate, furfuryl alcohol, reso Graphite carbon is formed by a carbonation reaction selected from lecinol-formaldehyde, sugar, a compound represented by the general formula CH ₂ = CRR ', wherein R and R' are alkyl or aryl groups or mesophase pitch Electrode catalyst for a fuel cell, characterized in that manufactured using a carbon precursor. The method of claim 1, wherein the active metal is platinum (Pt), ruthenium (Ru), rhodium (Rh), molybdenum (Mo), osmium (Os), iridium (Ir), rhenium (Re), palladium (Pd), Vanadium (V), cobalt (Co), tungsten (W), platinum-ruthenium (Pt-Ru) alloys, Pt-Ru-Rh alloys, Pt-Ru-Co-W alloys or Pt-Ru-Mo-W alloys An electrode catalyst for a fuel cell, characterized in that. delete a) dissolving a water-soluble salt of a metal having catalytic activity in water; b) injecting an aqueous slurry of a carbon structure with uniformly arranged uniform pores into a reaction vessel and mixing with an aqueous solution of a water-soluble metal salt; c) adjusting the pH of the reaction solution to 8-9 by adding a basic or acidic aqueous solution; d) adding a reducing agent to the reaction solution to form a precipitate; And f) recovering the catalyst, the method of producing a catalyst for a fuel cell according to any one of claims 1 to 3. The method of claim 5, wherein step b) further comprises the step of diluting the water-soluble metal salt concentration to 1mM to 3mM, wherein the reducing agent of step d) is NaBH ₄ , LiBH ₄ or AlBH ₄ aqueous solution A method for producing a catalyst for a fuel cell.

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