KR20050116171A - Bimodal pourus carbon structure, method for preparing the same, and catalyst for fuel cell using the same - Google Patents

Abstract

The present invention relates to a double porous carbon structure, a method for producing the same, and a fuel cell catalyst using the same. The biporous carbon structure according to the present invention is surrounded by mesoporous walls, has three-dimensional interconnections, and has uniform macropores arranged regularly. The bi-porous carbon structure comprises a meso-sized colo within the voids of the macro particle materials, mixing the macro-sized monodisperse particle material with a colloidal dispersion of meso-size particle material and aligning the macro-size particle material by self-assembly. This month, the particles are aligned and the aligned macro particles are removed to form a macro porous template surrounded by templated aggregates of mesosize particle material, and a carbon precursor solution in the pores of the porous mesosize particle material of the macro porous template. It is prepared by injecting and carbonizing, followed by removing the mesosize particle material of the macro porous template. Such a carbon structure can be used for electrode catalysts for fuel cells.

Description

Bi-porous carbon structure, a method of manufacturing the same, and a catalyst for fuel cell using the same {BIMODAL POURUS CARBON STRUCTURE, METHOD FOR PREPARING THE SAME, AND CATALYST FOR FUEL CELL USING THE SAME}

FIELD OF THE INVENTION The present invention relates to a dual porous carbon structure, a method for preparing the same, and a catalyst for a fuel cell using the same, and more particularly, uniform macropores surrounded by mesoporous walls, three-dimensionally interconnected, and regularly aligned. It relates to a double porous carbon structure having a, a method for producing the same and a catalyst for a fuel cell using the same.

Porous materials can be classified into three types, micropores (<2nm), mesopores (2-50nm), and macropores (> 50nm), depending on the diameter size of the pores. In addition, the control of pore size allows porous materials to be used in many applications, including catalysts, separation systems, low dielectric constant materials, hydrogen storage materials, and photonic crystals, which are of great interest.

Porous materials include inorganic materials, metals, polymers, carbon, and the like, among which carbon has excellent chemical, mechanical and thermal stability, and is a useful material that can be used in various ways.

In particular, porous carbon is an important material in low temperature polymer electrolyte membrane fuel cells because of its surface properties, ion conductivity, corrosion resistance and low cost. Accordingly, various kinds and types of carbon materials are currently used, but mainly high surface area activated carbon and carbon black are only used as supports for preparing metal catalysts. Specifically, carbon black, Vulcan XC-72, is commonly used as a support material for electrode catalysts in fuel cells. In fact, a commercially available E-TEK catalyst is a Pt-Ru alloy supported on Vulcan XC-72.

Recently, several different carbon materials such as mesostructured carbon, graphite carbon nanofibers, and mesocarbon microbeads have been developed for higher dispersion of metal catalysts. And as a support of Pt or Pt-Ru alloy catalysts for improved synergy.

However, it is still a very difficult task to synthesize carbon materials having a high surface area and a completely interconnected uniform porous structure.

The use of templates has been proposed to produce porous materials. As templates, colloidal crystalline arrays based on ordered aggregates of spherical silica or latex polymer nanoparticles are used. In addition, aligned mesoporous M41S silica materials are prepared using micelle arrays of surfactant molecules as a structure-directing agent for silica polymerization (CT Kresege, et al., Nature 1992, 359). , 710).

Recently, there have been remarkable advances in synthesizing carbon with regularly ordered porosity by template replication with zeolites, mesoporous materials and colloidal crystals. In this synthesis, a carbon precursor is initially injected into a sacrificial solid porous silica mold, which is then carbonized under a non-oxidizing condition and then dissolved by removing the silica mold in HF or NaOH solution to remove the porous carbon structure. Prepared. During the replication process, the pores and walls of the host (silica mold) were converted into walls and pores of the prepared porous carbon structures, respectively. Thus, host scaffold materials are required to have interconnected pore systems, which enable structural integrity of the templated carbon after host removal. Some of the regularly ordered porous carbons obtained through this method show their availability as catalyst supports for fuel cells or as double layer electric capacitors (EDLC). However, the carbon produced here consists of a single pore.

More recently, rapidly expanding research efforts in this field are placing greater pressure on the production of more complex hierarchical multistructured porous carbon.

In this regard, carbon foams of double-structured mesocells consisting of uniform mesopores and ultralarge mesopores have been reported. In addition, methods have been reported of replicating carbon capsules having hollow macroporous core / mesoporous shells via nanocasting of solid core / mesoporous shell silica. It has also been reported that carbon pillars having a hierarchically fully interconnected porosity are synthesized by template replication of meso-macroporous silica pillars as host skeleton. However, the pores in these carbons were not distributed in a regularly ordered manner.

 Thus, the inventors are surrounded by mesoporous walls and three-dimensionally interconnected, studying the new type of carbon with excellent porous structure in which the pores are completely interconnected and distributed in a regular array. The present invention has been completed and found that a dual porous carbon structure having a uniformly aligned macropore can be obtained.

Accordingly, it is a first object of the present invention to provide a dual porous carbon structure composed of regularly aligned macropores and mesopores.

It is also a second object of the present invention to provide a method for producing a regularly aligned double porous carbon structure.

In addition, a third object of the present invention is to provide an electrode catalyst for a fuel cell using a regularly aligned double porous carbon structure.

To achieve the first object, the present invention provides a biporous carbon structure having uniform macropores surrounded by walls of mesoporous structure, interconnected three-dimensionally and regularly aligned.

The macropores of the double porous carbon structures have a diameter of 100 to 500 nm, and mesopores preferably have a diameter of 5 to 50 nm.

In order to achieve the second object of the present invention, the present invention

a) mixing the macroscale monodisperse particulate material with a colloidal dispersion of mesoscale particulate material;

b) arranging the meso-sized colloidal particle material within the pores of the macro-sized particles while arranging the macro-sized particle material by self-assembly;

c) removing the aligned macro particles to form a macro porous template surrounded by a templated aggregate of mesosize particle material;

d) injecting and carbonizing a carbon precursor into the pores between the mesosize particle material of the macroporous template; And

e) the formation of a bi-porous carbon structure surrounded by mesoporous walls, three-dimensionally interconnected, and regularly aligned uniform macropores, the method comprising removing the mesosize particle material of said macroporous template. It provides a manufacturing method.

In step a) of the manufacturing method according to the present invention, the macro-sized monodisperse particle material is preferably in a form that can form a certain gap when its shape is aligned, and particularly ideally, it is spherical. In addition, the material may be any material that can be selectively removed while remaining mesosize particle material contributing to forming mesoporous walls. Specifically, when the mesosize particle material is an inorganic material that is not oxidized, it may be an organic material that can be removed by oxidation, for example, solid polymer particles such as polystyrene, polymethyl methacrylate, and the like. It is also desirable that these materials have a uniform diameter in the range from 100 to 500 nm. Accordingly, spherical polystyrene having a uniform diameter in the range of 100 to 500 nm is most preferred as the macro-size monodisperse particle material. Synthesis of these materials is generally described by Roberts, JM; Linse, P .; Osteryoung, JG; Langmuir 1998, 14, 204 can be synthesized based on the method reported. Specifically, polystyrene spheres can be synthesized using an emulsifier-free emulsion polymerization method using styrene as a monomer and potassium persulfate as an initiator and no surfactant in aqueous solution.

Another component of step a) mesosize particulate material may be spherical or rod-shaped, and any material that is not removed by the method of removing the macrosize particle material, in particular an inorganic material such as silica, Al Metal oxides such as ₂ O ₃ , TiO _2, and the like or metals such as copper, silver, gold, and the like. The mesosize particulate material preferably has a uniform diameter of 5 to 50 nm. Therefore, spherical silica having a uniform diameter of 5 to 50 nm is most preferred as meso-size particle material. These are also described in Stober, W .; Fink, A .; Bohn, E. J. Colloid Inteer, Sci , 1968, 26, 62.

The macrosize particle material is mixed in the form of an aqueous dispersion solution and the mesosize particle material in the form of a colloidal dispersion, and the colloidal dispersion usually uses alcohol or water. In addition, the macro-sized particles dispersed in the aqueous solution and the meso-sized particles dispersed in the alcohol are mixed so that the particle weight ratio is 1.5: 1 to 2.0: 1.

In step b) of the manufacturing method of the present invention, the macro-size particle material is regularly aligned through a self-assembly method, and the meso-size particle material is densely aligned in the pores of the macro-size particle materials thus aligned.

An example of a method of self-assembly is possible by gradually evaporating and drying the dispersion medium for a sufficient time, and may also use auxiliary means such as sonication for initial uniform mixing with drying. Preferably the drying method is usually 4 to 7 days at 30 to 70 ℃ Gradually dry. Self-assembly works best with a diameter ratio between macro-sized spheres and meso-quick spheres of 10 or more, usually at room temperature without special devices, slowly drying and regularly self-assembling spherical particles mixed by capillary forces.

In step c) of the manufacturing method according to the present invention to form a wall of uniform macropores that are three-dimensionally interconnected and regularly aligned through the method of removing the macro-size particle material without removing the meso-size particle material A macroporous template is formed that is surrounded by a templated aggregate of mesosize particle material.

The macroporous template formed in this step provides mesopores in which the voids between the mesosize particulate material therein are also completely interconnected.

As a method of removing the macro-size particle material without removing the meso-size particle material, an etching method or a baking method by a solution having selectivity for two particles may be used. For example, when the macrosize particle material is polystyrene and the mesosize particle material is silica, the macroporous template is formed by removing the macrosize particle material by firing at 450 to 550 ° C. for 6 to 7 hours. . Alternatively, the macroporous template may be formed by removing the macro-sized particle material by etching at room temperature with toluene or dimethylformamide solution.

In step d) of the manufacturing method according to the present invention, the carbon precursor is injected and carbonized between the pores of the meso-size particle material of the macroporous template formed in step c).

The carbon precursor may be divinylbenzene, acrylonitrile, vinyl chloride, vinyl acetate, styrene, methacrylate, methyl methacrylate, ethylene glycol dimethacrylate, urea, melamine, or CH ₂ = Monomers such as CRR '(where R and R' represent alkyl or aryl groups) include azobisisobutyronitrile (AIBN), t-butyl peracetate, benzoyl peroxide (BPO), acetyl Polymers prepared by addition polymerization using acetyl peroxide or lauryl peroxide initiators, phenol-formaldehyde, phenol, furfuryl alcohol, resorcinol-formaldehyde ( In a polymer or mesophase pitch produced by condensation polymerization of a monomer such as RF), aldehyde, sucrose, glucose or xylose using an acid catalyst such as sulfuric acid or hydrochloric acid. The selection or non-graphitizing carbon include other carbon precursor to form a (graphitic carbon) by the carbonization reaction.

The addition polymerizable monomers may be used alone or in a mixture of two or more monomers. At this time, the molar ratio of the monomer and the initiator is 15: 1 to 35: 1 but ideally 25: 1. The condensation polymerizable monomers may also be used alone or as a mixture of two or more monomers, wherein the molar ratio of the monomers and acid catalyst is about 5: 1 to 15: 1 and ideally 10: 1.

The monomer and initiator or monomer and acid catalyst mixture are injected in an amount of 20 to 30% by volume relative to the macroporous template, and the injection of the mixture can be in liquid or gaseous phase. More specifically, the mixture may be added in the liquid phase to the template or the solid precursor material in vacuo may be heated to inject into the pores of the mesosize particle material of the template in the gas phase. Here, the impregnation method may be used as the injection method.

The macroporous template into which the mixture of the addition-polymerizable monomer and the required initiator are injected is polymerized under other known optimum conditions depending on the polymerizable compound used, but is preferably polymerized for 3 to 30 hours at a temperature of 60 to 90 ° C. React. In the case of the condensation-polymerizable monomer and the acid catalyst mixture, the polymerization may be carried out under other known optimum conditions depending on the condensation-polymerizable compound used, but is preferably polymerized at a temperature of 80 to 140 ° C for 3 to 30 hours. In both cases, upon completion of the polymerization, a mesosize particulate-polymer composite is obtained. The acid, which is a catalyst during the condensation polymerization, may form an acid site on the surface of the meso-sized particle material to show the acid catalyst characteristics of the template itself, or to add an acid catalyst (hydrochloric acid, sulfuric acid, etc.) from the outside to act as a catalyst during the condensation reaction of the polymer monomer. It may be.

The porous macro template into which the carbon precursor polymer is injected is heat-treated at a temperature of 800 to 1500 ° C. for 5 to 15 hours under an inert gas such as Ar or N ₂ to carbonize the polymer to obtain a meso-size particle-carbon composite. . At this time, the temperature increase rate is in the range of 1 ° C / minute to 10 ° C / minute.

In step e) of the manufacturing method according to the present invention uses a method that can remove the meso-size particle material without modifying the mesopores formed to remove the meso-size particle material. As such a method, an etching method or a firing method may be used. The etching method is etched with an HF solution, a NaOH solution or a KOH solution, and the firing method is baked at a temperature of 300 to 550 ° C. for 5 to 8 hours. Specifically, when the meso-size particle material is silica, it is removed by etching with HF solution, NaOH solution or KOH solution, filtered and washed and dried at 70 to 80 ° C.

Eventually, the carbon structure according to the present invention through the above method has mesopores through the removal of mesosize particle material, and has macropores through the removal of macrosize particle material.

In addition, in order to achieve the third object of the present invention, the present invention uses a double porous carbon structure having a uniform macropore surrounded by mesoporous walls, interconnected in three dimensions, and regularly aligned. A catalyst for a fuel cell is prepared.

The electrode catalyst for a fuel cell according to the present invention is a fuel cell that uses a liquid alcohol such as a direct methanol fuel cell (DMFC) and a direct ethanol fuel cell (DEFC) as a direct fuel, as well as oxidation (fuel electrode) and reduction of a hydrogen fuel cell ( Air cathode) electrode can also be applied.

The active metal used in the electrode catalyst for a fuel cell according to 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), rhodium (Rh) ), Molybdenum (Mo), osmium (Os), iridium (Ir), rhenium (Re), palladium (Pd), vanadium (V), cobalt (Co) and tungsten (W) It includes. 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 20 times or more of 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 6 times per unit mass as 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, thereby making it possible to efficiently use expensive precious metals. Also advantageous. For example, platinum for fuel cells supported by a bi-porous carbon structure surrounded by walls of mesoporous structures, interconnected three-dimensionally and having uniformly aligned uniform macropores, according to the present invention. Ruthenium / carbon electrodes reduce the amount of porous carbon to 20 wt% or less of the total catalyst weight (approximately 50 % Reduction) Even if the catalyst is prepared, it is possible to prepare a catalyst having better activity than Pt-Ru (molar ratio 1: 1) catalyst (E-TEK, 60 wt.% Total metal supported), which is a commercially available electrode catalyst.

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. Since the catalyst of has 80% or more of the amount of metal supported, since the amount of the support used to support the same amount of metal is only 1/2, the above-mentioned cracking phenomenon can be prevented because a small amount of catalyst is used entirely. . 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.

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

1 is a view schematically showing a cross-section of a double porous carbon structure according to the present invention, Figure 2 is a SEM photograph taken at different magnifications of the double porous carbon structure according to the present invention.

Referring to FIG. 1, in the carbon structure according to the present invention, macropores 1 and mesopores 2 are regularly arranged, and in particular, mesopores 2 are formed on the wall between the macropores 1. This structure is a double porous structure in which these structures are arranged periodically.

Referring to FIG. 2, it can be seen that three round holes are shown as black dots in the macropores represented by one large circle in the three-dimensional structure of carbon according to the present invention. These holes are connecting pores, through which one macropore connects to three neighboring macropores below it. Thus, it can be seen that the macropores are three-dimensionally interconnected. Here, the diameter of the macropores is approximately 320 nm and the size of the mesopores is approximately 10 nm.

Figure 3 shows a representative example step by step of the method for producing a double porous carbon structure according to the second object of the present invention.

Referring to FIG. 3, in order to produce carbon according to the present invention, first, a macroscopic spherical monodisperse particle material 3 is mixed into a colloidal dispersion of mesosize particle material 4. The state after mixing was shown by (10) in FIG. 3 (step a).

Here, spherical monodisperse polystyrene may be used as the macro-sized spherical particle material 3, and spherical silica particles may be used as the meso-sized particle material 4.

The macropore size of the carbon structure obtained by controlling the size of the macro-sized spherical particle material 3 can be determined, and the size of the mesopore is controlled by controlling the size of the meso-size particle material 4. Can be determined. In addition, the shape of the mesopores may vary depending on the shape of the mesosize particle material (4). Preferably, the diameter of the macro-sized spherical particle material 3 is in the range of 100 to 500 nm, and the meso-sized particle material 4 is spherical and its size is 5 to 50 nm.

The macrosize particle material 3 is then aligned and self-assembled so that the mesosize particle material 4 is aligned and densely filled between the pores of the macrosize particle material 3. Self-assembly results in the mixture being 4-7 days at 30-70 ° C. Gradually drying. After drying, the macro-size particle material 3 and the meso-size particle material 4 are regularly arranged as shown in (20) of FIG. 3 (step b).

In the above, as the drying proceeds, as the mesosize particle material 4 is regularly densely filled into the voids of the macrosize particle material 3, the mesosize particle material between the voids of the macrosize particle material 3 ( 4) becomes a gel state.

The subsequent step is to remove the aligned macro particles by a method such as etching or firing. After removal of the aligned macro particles, it is the same as (30) of FIG. 3 (step c). For example, when the macro particle material is polystyrene, the dried material is calcined at 450 to 550 ° C. for 6 to 7 hours to form a macro porous template. 3 shows a macroporous template formed through the firing method.

As shown in (30) of FIG. 3, as the macro particle material 3 is removed, a macro-sized pore 1 is formed, and a meso-size particle material 4 is formed around the macro pore 1. To form walls. That is, a template is formed having walls of mesosize particle material 4 around the macropores 1. Eventually, meso-size particle materials serve as a framework for the macroporous structure.

In addition, methods such as firing reinforce the framework structure as the mesosize particle materials 4 are weakly sintered at their contact points. Particularly, in the case of silica, heating at about 550 ° C. for about 3 hours is sufficient, and in the case of polystyrene, the firing treatment is sufficient at 450 ° C. or higher.

Subsequently, the carbon precursor solution is injected into the pores of the meso-sized particle material of the macroporous template, followed by carbonization by high temperature heat treatment at 800 to 1500 ° C. under an inert gas (Ar, N _2, etc.) for 5 to 15 hours. . The state after carbonization is shown by (40) of FIG. 3 (step d).

As shown in (40) of FIG. 3, the carbon precursor solution is penetrated into the gap between the mesosize particle material 4 due to the capillary effect, not the macropores 1, and the carbon precursor solution 5 It is shown in black in the figure.

 Finally, the mesosize particle material 4 is removed. The removal of the mesosize particle material 4 is shown by (50) in FIG. 3 (step e). 3 (50) shows a case where an etching method is used as the removal method. As can be seen from the figure, through the removal of the mesosize particle material 4 through etching, it is possible to obtain a biporous carbon structure in which mesopores 2 are formed in the gaps of the macropores 1.

Carbon formed by the above method is highly available as a catalyst support for obtaining high catalytic activity in two respects due to its double porous structure and its very large interconnected porous structure.

Accordingly, the biporous carbon structure composed of a macropore having a diameter of 100 to 500 nm and mesopores having a size of 5 to 50 nm that is filled in the gaps of the macropores to form a wall of the macropores is periodically aligned. It can be used as a catalyst support for fuel cells.

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

Example 1

Fabrication of Carbon Structures with Double Porous Structure

In a 2 L flask, 400 ml (4.3 wt%) of polystyrene sphere aqueous dispersion having a diameter of about 340 nm was mixed with 700 ml (1.2 wt% of colloidal dispersion) of spherical silica having a size of about 20 nm. The mixture was then dried at 60 ° C. for 7 days. Subsequently, about 22 g of the resulting dried product was fired in a furnace in an air atmosphere at 550 ° C. for 6.5 hours to form 8.5 g of macroporous template. In the macroporous template, the diameter of the macropores was 330 nm on average, and the silica particles were 13 nm on average. The template was then dried under vacuum at 70 ° C. for 2 hours. Next, 4 ml of divinylbenzene (DVB) as a carbon precursor was mixed at a ratio of 0.1845 g of azobisisobutyronitrile (AIBN), a free radical initiator, to 4 ml of the solution (the molar ratio of DVB / AIBN was approximately 24). 2.0 g of the porous template was added thereto, and then polymerized at a temperature of 70 ° C. for 12 hours. The carbon precursor polymer was then allowed to fill the pores of the mesosize silica. This was then carbonized by heating at 1000 ° C. for 7 hours under argon gas flow. The obtained porous silica-carbon composite material was put in 100 ml of an aqueous 48% HF solution to dissolve silica to obtain about 0.2 g of a carbon structure having a double porous structure having an average macropore size of about 317 nm and an average mesopore size of 10 nm.

The SEM photograph of the macroporous template is shown in FIG. 4, and the SEM photograph of the double porous carbon structure is shown in FIG. 2. As shown in Figures 4 and 2, it can be seen that the macroporous template and the double porous carbon structure obtained according to the present invention have a very regular structure.

Example 2

In the same manner as in Example 1, except that the diameter of the monodisperse polystyrene sphere (about 360nm) and silica (diameter about 23nm) is different, the average macropore size is about 324nm and the average mesopore size is 19nm About 0.2 g of carbon structure was obtained.

Example 3

In the same manner as in Example 1, except that the diameter of the monodisperse polystyrene sphere (about 370nm) and the silica (about 30nm in diameter) are different, the average macropore size is about 328nm and the average mesopore size is 27nm About 0.2 g of carbon structure was obtained.

The carbon structures obtained in Examples 1 to 3 are shown in FIG. 6. Figure 6 (a) is a SEM photograph of the macroporous template obtained in Example 2, (b) is a SEM photograph of the double porous carbon structure obtained in Example 2, (c) is in Example 3 The obtained biporous carbon structure is shown by SEM photographs, and (d) shows the TEM photograph of the biporous carbon structure obtained in Example 1.

As also confirmed through FIG. 6, it was confirmed that the carbon structure according to the present invention is a regular double porous structure.

Example 4

Preparation of Carbon Supported Pt-Ru Alloy Catalyst

Carbon-supported Pt-Ru alloy catalyst As the metal precursor using H ₂ PtCl ₆ .6H ₂ O (Aldrich) and RuCl ₃ .xH ₂ O (Aldrich), and using as the reducing agent NaBH ₄ was synthesized at room temperature.

That is, equimolar (2 × 10 ^-3 mol) of _{H 2 PtCl 6 .6H 2 O (} 40.88% Pt) 1.0976g and _{RuCl 3 .xH 2 O (40.71%} Ru) 0.4965g were dissolved in deionized water 100㎖ metal salt The solution was prepared. 0.1481 g of the carbon structure obtained in Example 1) was suspended in 100 mL of deionized water and stirred for 1 hour to form a uniform carbon slurry. Subsequently, 100 ml of the carbon slurry was added to 100 ml of the metal salt solution, stirred for about 30 minutes, and 2.8 L of deionized water was added to dilute the metal salt-carbon mixed solution, followed by stirring for about 1 hour. The pH of the mixed solution was adjusted to about 8 using a 3.0 M NaOH solution, and 50 ml of excess NaBH ₄ solution (NaBH ₄ / metal molar ratio was approximately 10) was rapidly added to the carbon-metal salt mixed solution under vigorous stirring for 2 hours. The metal salt was reduced by stirring at ambient temperature over to prepare a Pt ₅₀ -Ru ₅₀ catalyst with 80% by weight metal loading based on the total weight of the catalyst.

In addition, a TEM photograph of the catalyst is shown in FIG. 7. As shown in FIG. 7, it can be seen that the small, spherical uniform black dots corresponding to the Pt-Ru alloy nanoparticles are uniformly distributed. The particle size measured directly from the TEM photograph in a randomly selected region for the sample was approximately 2-3 nm. This was further confirmed by mean particle size analysis from the (220) X-ray diffraction peak of the Pt fcc grating by Scharrer's equation.

Comparative Example 1

Using the 0.3949 g of Vulcan XC-72 carbon black of Cabot Co. as the carbon support, the same method as in Example 4 was repeated to obtain 0.984 g of Pt-Ru alloy catalyst.

Comparative Example 2

Commercially available E-TEK catalysts were used. (Manufacturer E-TEK)

Comparative Example 3

Method of manufacturing macro porous carbon structure

According to the method described in Korean Patent Application No. 2000-57082, a macroporous carbon structure used as a support for an electrode catalyst for a fuel cell was prepared, the contents of which are incorporated herein by reference. Specifically, 10 g of spherical silica having a diameter in the range of approximately 370 nm was evenly dispersed in a 200 ml aqueous solution of 1 L beaker, dried at 40 ° C. to self-assemble on an aqueous solution, and then the dried silica material was heated to 800 ° C. A colloidal crystal template was made, 4 mL of DVB and 0.1845 g of AIBN were injected into the pores between the spherical silicas forming the template, and then polymerized at 70 ° C. Subsequently, the silica-carbon precursor composite was carbonized at about 1000 ° C. under an inert gas atmosphere to obtain a carbon-silica template composite, and then uniformly arranged with a diameter of about 320 nm by removing only the template using 48% HF. A porous carbon structure with fine pores was obtained.

Preparation of Carbon Supported Pt-Ru Alloy Catalyst

The same procedure as in Example 4 was repeated using 0.148 g of the macroporous carbon structure obtained above as the carbon support to obtain 0.74 g of a Pt-Ru alloy catalyst.

Test Example 1

Approximately 100 mg of each of the macroporous template and the biporous carbon structure prepared in each step of Example 1 were weighed to degas each sample for 4-6 hours from 423 K to 20 μTorr, followed by Micrometries at 77 K. Adsorption tests were performed using an ASAP 2010 gas adsorption analyzer. The results are shown as adsorption isotherms in FIG. 5. At this time, the surface area, pore volume and pore size distribution of the sample were measured using the BET equation and the BJH method using the volume of the adsorbed nitrogen gas molecules, and the results are shown in Table 1.

Macroporous template Double porous carbon structure BET surface area 160㎡ / g 465㎡ / g Average Pore Size Distribution 3.4 nm 9.5 nm Full pore volume 0.290ml / g 1.32ml / g

The isotherms of the macroporous template and the biporous carbon structure prepared in the present invention correspond to type IV with type H ₂ hysteresis according to the IUPAC definition, which typically represents the properties of framework mesopores. Mesopores occurred in the porous carbon walls obtained by dissolution of the silica particles and gaps between the aggregated spherical silica particles of the porous silica template. An interesting change in mesopore origin was also seen in the process of replication from porous silica template to porous carbon accompanied by a change in mesopore size in FIG. 5.

In the silica-carbon composites, the mesoporosity of the silica template disappeared as the mesopores were completely filled by carbon as shown in the isothermal and corresponding pore size distributions.

Test Example 2

In order to evaluate the electrode catalyst activity of the carbon-supported catalysts obtained in Examples 4 and Comparative Examples 1 and 2, a DMFC (Direct Methanol Fuel Cell) unit cell having a 2 cm 2 catalyst area was used, and a potentiometer (WMPG- 1000) and measured at 30 ° C. and 70 ° C., and the results are shown in Table 2 and FIGS. 8 and 9. The potentiometer records the cell potential under constant current conditions. In this case, Johnson Matthey Pt Black (5.0 mg / cm 2) as a catalyst, a catalyst obtained in Examples 4 and Comparative Examples 1 and 2 as an anode, and Nafion 117 (DuPont) as an electrolyte were used. MEA (membrane electrode assembly) was prepared by hot-pressing pretreated Nafion 117 with anode and cathode catalyst on each side. Catalyst loadings at the metal based anode and cathode were 2.0 mg / cm 3 and 5.0 mg / cm 3, respectively. The Nafion 117 membrane was pretreated by boiling in 3% by weight H ₂ O ₂ for 1 hour and then in 0.5MH ₂ SO ₄ for 1 hour. The single cell test fixture consisted of two copper end plates and two graphite plates with a lip-channel pattern to provide a methanol passage to the anode and an oxygen gas passage to the cathode. A 2.0 M methanol solution was provided to the anode by a masterplex liquid micro-pump at a rate of 1.0 mL / min and dry O ₂ was injected into the cathode at a rate of 300 mL / min using a flow meter.

 division Metal loading (% by weight ^{* 1} )  30 ℃ 70 ℃ Current density (0.5V) Power density Current density (0.5 V) Power density Example 4 80 40 mA / ㎠ 70 mW / ㎠ 190 mA / ㎠ 190 mW / ㎠ Comparative Example 1 60 7.5 mA / ㎠ 32 mW / ㎠ 23 mA / ㎠ 106 mW / ㎠ Comparative Example 2 60 10 mA / ㎠ 39 mW / ㎠ 54 mA / ㎠ 121 mW / ㎠

1.Weight%: Based on the total weight of the chock

Test Example 3

In order to evaluate the electrode catalyst activity of the carbon supported catalyst obtained in Example 4 and Comparative Examples 1 and 3, it was tested in the same manner as in Test Example 2, the results are shown in Table 3 and FIG.

 division Metal loading (% by weight)  30 ℃ Current density (0.5V) Power density Example 4 80 40 mA / ㎠ 70 mW / ㎠ Comparative Example 2 60 10 mA / ㎠ 38 mW / ㎠ Comparative Example 3 80 12.5 mA / ㎠ 44 mW / ㎠

As can be seen in Table 2, the metal loading of the double porous carbon structure according to the present invention (Example 4) is 80% by weight, while the metal loading of Comparative Example 1 using Vulcan XC-72 carbon is 60% by weight. It was. This indicates that the bi-porous carbon structure according to the present invention is capable of higher metal loading, and has high utility in DMFC where high catalyst loading is essential.

The evaluation results of the electrode catalyst activity of the carbon supported catalyst measured through the unit cell of a direct methanol fuel cell (DMFC) are shown in Tables 2 and 3 and FIGS. 8 and 9, at 30 ° C., Example 4 was 0.5V. Showed a current density of 40 mA / cm 2, while the current densities of the VC catalyst of Comparative Example 1 and the E-TEK catalyst of Comparative Example 2 were 7.5 and 10 mA / cm 2, respectively. In addition, the maximum power density shows that the catalyst prepared in the present invention exhibits a higher maximum power density (70 mW / cm 2) than other catalysts. In addition, similar results were obtained at 70 ° C. That is, while the current density of the catalyst (Example 4) according to the present invention was 190 mA / cm 2, the current densities of Comparative Examples 1 and 2 were 23 mA / cm 2 and 54 mA / cm 2, respectively, and the maximum power density was also compared with that of Example 4. Comparing Example 2, it was found to be about 57% higher.

All visible activity data was measured several times and was reproducible within experimental error. In particular, the catalyst according to the invention remained stable and maintained constant catalytic activity for at least 150 hours in a unit cell.

Interestingly, the catalyst of Vulcan XC-72 supported Comparative Example 1 prepared under the same conditions as the catalyst according to the present invention showed lower oxidation activity than the commercially available E-TEK catalyst (Comparative Example 2) also supported on Vulcan carbon. . This indicates that the Pt-Ru alloy catalyst produced in-house in this experiment is less excellent than the E-TEK catalyst in terms of methanol oxidation activity, since the same Vulcan carbon was used as a support for both cases. . Even in this case, the catalyst according to the invention showed better performance than the E-TEK counterpart. Thus, this increase in activity can contribute solely to the very large supporting effect of porous carbon. This is a significant advance in DMFC.

In addition, the carbon structure according to the present invention (Example 4), which is surrounded by walls of mesoporous structure, three-dimensionally interconnected, and with uniformly aligned uniform macropores, is also a regular lattice of the same size. Compared with macroporous carbon (Comparative Example 3) having a structure but no mesoporous walls, it shows better catalytic activity as shown in FIG. 9. In other words, the current density and the maximum power density were nearly doubled at 30 ° C. These results indicate the importance of smaller mesopore walls, which allows for a higher degree of catalyst dispersion.

As described above, the carbon structure according to the present invention has a structure having uniform macropores surrounded by walls of mesoporous structure, interconnected three-dimensionally and regularly aligned, and thus the electrode using the carbon structure. It can be seen that the activity of the catalyst is significantly improved.

This improvement is due to the unique structural properties of the carbon structure according to the invention. That is because of the higher surface area and larger pore volume and three-dimensionally interconnected well-assembled macro and meso double porosity. In addition, the carbon structure according to the present invention having a uniformly distributed pore of uniform size has a higher characteristic of transport and diffusion of fuel and products in the catalyst than Vulcan carbon having randomly distributed pores of various sizes due to its structural characteristics. To facilitate. Thus, catalyst dispersion is improved and further has high catalytic activity.

The carbon structure having such a structure can also be adjusted to increase or decrease the amount of active metal supported in the preparation of the catalyst, and thus has high utility.

In addition, the carbon structure according to the present invention can be applied in various fields in which efficient delivery and high surface area are very large advantages such as in a direct methanol fuel cell.

1 is a cross-sectional view schematically showing the structure of a carbon structure having a double porous structure according to the present invention.

2 is a SEM photograph of a carbon structure having a double porous structure according to the present invention.

3 is a diagram schematically showing an example of a method of manufacturing a double porous carbon structure according to the present invention.

4 is a SEM photograph of a macroporous template surrounded by a templated aggregate of mesosize particle material for the production of a biporous carbon structure in accordance with the present invention.

5 is a graph showing the N ₂ adsorption and desorption performance of the double porous carbon structure according to the present invention.

6a to 6d are SEM and TEM photographs of the macroporous template and the obtained carbon structure for obtaining the desired carbon structure in the embodiment according to the present invention.

7 is a TEM photograph of a catalyst on which a PtRu metal is supported on a bi-porous carbon structure according to the present invention.

8A is a graph showing the performance at 30 ° C. of a direct methanol fuel cell using a catalyst using a double porous carbon structure according to the present invention, and FIG. 8B is a catalyst using the double porous carbon structure according to the present invention as a support. Is a graph showing the performance of the direct methanol fuel cell at 70 ° C.

9 is a graph showing the results of comparing the performance of the catalyst using the double porous carbon structure as a support and the catalyst using a macroporous carbon structure as a support according to the present invention.

* Short description of drawing symbols *

1. Macropores 2. Mesopores

3. Polystyrene Sphere 4. Silica Particles

5. Carbon precursor solution 10. Mixed solution

20. Buildings 30. Macro Porous Templates

40. Composite 50. Carbon Structure

Claims (16)

A biporous carbon structure surrounded by walls of mesoporous structure, three-dimensionally interconnected, and having uniformly aligned uniform macropores. The biporous carbon structure according to claim 1, wherein the macropores of the biporous carbon structures have a diameter of 100 to 500 nm and the mesopores have a diameter of 5 to 50 nm. a) mixing the macroscale monodisperse particulate material with a colloidal dispersion of mesoscale particulate material; b) aligning the meso-sized colloidal particle material within the pores of the macro-sized particles while aligning the macro-sized particle material by self-assembly; c) removing the aligned macro particles to form a macro porous template surrounded by a templated aggregate of mesosize particle material; d) injecting and carbonizing a carbon precursor into the pores between the mesosize particle material of the macroporous template; And e) a bi-porous carbon having a uniform macropore that is surrounded by walls of three-dimensionally interconnected, regularly aligned, mesoporous structure comprising removing the mesosize particle material of the macroporous template. Method for producing a structure. The method of claim 3, wherein in step a), the macrosize monodisperse particle material is spherical and has a size ranging from 100 to 500 nm and is a material of a material that can be removed in step c), and the mesosize particle material is spherical or Method of producing a bi-porous carbon structure, characterized in that the rod-shaped material having a size in the range of 5 to 50nm can be removed in step e). 5. The method of claim 4, wherein the macroscopic particulate material is an organic material and the mesosize particulate material is an inorganic material. The method of claim 5, wherein the macro-sized particulate material is polystyrene spheres and the meso-sized particulate material is silica spheres. The method of claim 3, wherein step b) is carried out by self-assembly by gradually drying at 30 to 70 ℃ for 4 to 7 days. 4. The method of claim 3, wherein step c) is performed by removing the macrosize particle material by firing or etching. The method of claim 8, wherein the firing method is performed by heating in an atmospheric atmosphere for 6 to 7 hours at 450 to 550 ℃.  The method of claim 8, wherein the etching method is performed by immersing in a toluene or dimethylformamide solution at room temperature. The method of claim 3, wherein the carbon precursor in step d) is divinylbenzene, acrylonitrile, vinyl chloride, vinyl acetate, styrene, methacrylate, methyl methacrylate, ethylene glycol dimethacrylate, urea , Melamine or CH ₂ = CRR '(where R and R' represent alkyl or aryl groups), such as azobisisobutyronitrile (AIBN), t-butyl peracetate , Polymers prepared by addition polymerization using benzoyl peroxide (BPO), acetyl peroxide, or lauryl peroxide initiators, phenol-formaldehyde, phenol, furfuryl alcohol ) Or polymers or mesophases prepared by condensation polymerization of monomers such as resorcinol-formaldehyde (RF), aldehydes, sucrose, glucose or xylose with an acid catalyst such as sulfuric acid or hydrochloric acid. A method of producing a bi-porous carbon structure selected from mesophase pitch or from other carbon precursors that form graphitic carbon by a carbonation reaction. The method of claim 3, wherein step d) is performed by high temperature heat treatment of the porous macro template into which the carbon precursor polymer is injected at a temperature of 800 to 1500 ° C. for 5 to 15 hours under an inert gas. Way. The method of claim 3, wherein step e) is performed by etching with HF solution, NaOH solution or KOH solution to remove meso-size particulate matter or by baking for 5 to 8 hours at a temperature of 300 to 550 ° C. Method for producing a phosphorous double porous carbon structure. An electrode catalyst for a fuel cell comprising the double porous carbon structure according to claim 1 as a support. 15. The method of claim 14, wherein the electrode catalyst for the fuel cell is 5 to 95% by weight based on the total weight of the catalyst (Pt), ruthenium (Ru), rhodium (Rh), molybdenum (Mo), osmium (Os), iridium An electrode catalyst for a fuel cell comprising at least one active metal selected from the group consisting of (Ir), rhenium (Re), palladium (Pd), vanadium (V), cobalt (Co) and tungsten (W). 16. The fuel of claim 14 or 15, wherein the electrode catalyst for a fuel cell is used in a direct methanol fuel cell (DMFC), a direct ethanol fuel cell (DEFC), or a polymer electrolyte membrane fuel cell. Battery Electrode Catalyst.