KR20120087402A - Carboaceous nanomaterail and method of preparing the same - Google Patents

Abstract

PURPOSE: Carbon nanomaterials and a method for manufacturing the same are provided to improve the dispersibility of carbon nanofiber and to effectively support catalysts by introducing nitrogen into the carbon nanofiber. CONSTITUTION: Carbon nanomaterials include carbon nanofiber containing nitrogen. The nitrogen is doped to the carbon nanofiber. The content of the nitrogen in the carbon nanofiber is in a range between 0.5 and 10 atomic%. The ratio of nitrogen and carbon(N/C) in the carbon nanofiber is in a range between 1.0 and 5.0atomic%. The carbon nanofiber is a herringbone structure. The average diameter of the carbon nanofiber is in a range between 30 and 100nm. The specific surface area of the carbon nanofiber is in a range between 50 and 500m^2/g.

Description

Carbon Nano Materials and Methods for Making the Same {CARBOACEOUS NANOMATERAIL AND METHOD OF PREPARING THE SAME}

The present invention relates to a carbon nanomaterial and a method for producing the same, and more particularly, to a carbon nanomaterial and a method for producing the same, which are excellent in durability and capable of supporting a catalyst more efficiently.

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy.

This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

A number of research and development examples of electrode catalysts for fuel cells have been reported, but the current trends have focused on improving catalyst activity, and in recent years, many efforts have been made to improve durability in terms of practical use.

Existing catalysts have used supported catalysts to increase their inertness (activity per catalyst weight), but there is a difficulty in securing catalyst durability due to the destruction of the carrier structure in the process of increasing the carriers for high dispersion of the catalyst. For this reason, there have been cases of attempting to strengthen the support durability by graphitizing the carbon support, but due to the difficulty of the process and the difficulty of supporting the catalyst itself, there was a problem in terms of catalyst activity.

On the other hand, in the case of porous materials that are advantageous in terms of mass transfer such as mesoporous carbon, structural weakness is also a problem, and recently, a case of developing a catalyst utilizing nanoparticles or nanofibers as a support for a high specific surface area as an open surface has been reported. Although it has been reported, this situation is also difficult to obtain effective results due to the difficulty of supporting and dispersing the catalyst.

It is an object of the present invention to provide a carbon nanomaterial having excellent durability and capable of supporting a catalyst more efficiently and having excellent performance as a catalyst carrier.

The present invention also aims to provide a method for producing the carbon nanomaterial.

According to an embodiment of the present invention, a carbon nano material including carbon nanofibers including nitrogen is provided.

According to another embodiment of the invention, the step of introducing a nitrogen gas in the reactor, in the presence of a metal catalyst supported on a carrier; Heating the temperature while supplying a mixed gas of nitrogen gas and hydrogen gas to the reactor; And supplying a nitrogen-containing compound to the reactor.

The carbon nanomaterial according to the present invention has excellent durability and can carry a catalyst more efficiently, and thus has excellent performance as a catalyst carrier. The carbon nanomaterial of the present invention has an advantage of having excellent durability due to excellent crystallinity, carrying a catalyst more effectively, and improving dispersibility by introducing nitrogen into carbon nanofibers.

The carbon nanomaterial of the present invention is expected not only to be used as a support for a catalyst including an electrode catalyst of a fuel cell, but also to be used for introduction and development in various fields.

Figure 1 schematically shows the structure of a reactor used in the present invention.
Figure 2 shows the temperature and feed gas composition profile of the reaction process carried out in the embodiment of the present invention.
Figure 3 is a graph showing the N / C (atomic%) by the synthesis yield and elemental analysis results of the nitrogen-doped carbon nanotubes prepared according to Examples 1 to 11.
4 is a SEM photograph of nitrogen-doped carbon nanofibers prepared according to Examples 1-11.
5 is a graph showing the synthetic yield of carbon nanofibers prepared according to Examples 4, 7, 10 and 12 to 15.
6 is a SEM photograph of carbon nanofibers prepared according to Examples 4 and 12.
7 is a TG measurement graph for carbon nanofibers prepared according to Examples 2, 5, 7, 10, and 11.
8 is a graph of measuring the specific surface area of carbon nanofibers prepared according to Examples 1 to 11. FIG.
9 is a graph showing XPS (X-ray Photoelectron Spectroscopy) spectral results for nitrogen of the carbon nanofibers of Example 3. FIG.
FIG. 10 is a graph showing XPS (X-ray Photoelectron Spectroscopy) spectrum results for nitrogen of carbon nanofibers of Example 7.
11 is a graph showing the total nitrogen content of the carbon nanofibers prepared according to Examples 1 to 11 and the nitrogen content present on the surface of the carbon nanofibers.
12 shows the ratio of N / C atomic ratio and (B) component (graphite-like structure) / (A) component (pyridine-like structure) on the surface of carbon nanofibers prepared according to Examples 1 to 11. graph.
FIG. 13 is an X-ray diffraction (XRD) measurement graph of carbon nanofibers prepared according to Examples 1-11.
FIG. 14 is a graph showing the d002 interplanar distance and Lc (002) crystal size results of carbon nanofibers prepared according to Examples 1-11.
FIG. 15 is a graph showing the results of cyclic voltametry experiments measured using working electrodes using carbon materials of Examples 4, 7 and 10, and Comparative Examples 2-4. FIG.
FIG. 16 is a graph showing the results of oxygen reduction reaction experiments measured using working electrodes using the carbon materials of Examples 4, 7 and 10, and Comparative Examples 2 to 4. FIG.
FIG. 17 is a graph showing the results of cyclic voltametry experiments measured using working electrodes using catalysts prepared according to Examples 16-18 and Comparative Examples 5-6.
18 is a graph showing the results of oxygen reduction reaction experiments measured using working electrodes using catalysts prepared according to Examples 16-18 and Comparative Examples 5-6.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

The present invention relates to carbon nanomaterials. This carbon material includes carbon nanofibers containing nitrogen. In the carbon nanofibers, nitrogen may be present in the doped form and distributed throughout the crystal structure of the carbon nanofibers. As such, the presence of nitrogen in the doped form can prevent the outflow of nitrogen under severe conditions, and the nitrogen forms a structure with carbon nanofibers, thereby improving durability.

Nitrogen included in the carbon nanofibers may exist in various chemical states. That is, nitrogen may be inserted into the carbon structure constituting the carbon nanofibers and exist as a component A having a pyridine-like structure or a pyridine-like structure, and a graphite-like structure or pyrrole It may exist as B component which is a similar structure. It may also be present in combination with oxygen. When measuring carbon nanofibers containing nitrogen according to an embodiment of the present invention by X-ray photoelectron spectroscopy (XPS), the component ratio (B / A) of the B component and the A component is preferably 0.3 to 2.0, 1.0 to 2.0 are more preferable. When the component ratio (B / A) is included in the above range, it is effective in maintaining the structure of the carbon nanofibers while improving the activity for the oxygen reduction reaction.

The content of nitrogen in the carbon nanofibers may be 0.5 to 10 atomic%. When the content of nitrogen is included in the above range, it is possible to provide sufficient functionality by nitrogen doping and at the same time eliminate the structural vulnerability of the carbon nanofibers by nitrogen doping.

In the carbon nanofibers, the ratio (N / C) of nitrogen and carbon is preferably 1.0 to 5.0 atomic% . The higher the ratio of nitrogen, the greater the effect of imparting the effects of nitrogen, but too high the ratio of nitrogen acts as a defect in the carbon structure, resulting in weak crystallinity. When nitrogen is present in the above range compared to carbon, it is possible to obtain a doping effect of nitrogen in a highly crystalline structure.

The carbon nanofibers preferably have a herringbone structure. The herringbone structure means a state in which a graphene array is arranged at a constant angle in a V-shape about a fiber axis in carbon having a graphite structure having a crystalline structure. That is, the carbon nanofibers exhibit crystallinity. If the carbon nanofibers have a herringbone structure, the edges of the graphite may be exposed to the surface in abundance.

The carbon nanofibers have peaks of (002) plane at 2 to 20 ° when X-ray diffraction measurement using CuKα is performed. In addition, the interplanar distance d002 of the carbon nanofibers may be 0.340 to 0.356 nm, and the crystal size Lc (002) may be 1 to 7 nm.

The average diameter of the carbon nanofibers may be 10 to 100nm. When the average diameter of the carbon nanofibers is included in the above range, it is possible to obtain a high specific surface area as a carrier with structural durability.

The carbon nanofibers preferably have a specific surface area of 50 to 500m ² / g, more preferably having 70 to a specific surface area of 490m ² / g.

The carbon nano material may be manufactured by a manufacturing method according to another embodiment of the present invention. The production method includes introducing nitrogen gas in a reactor in the presence of a metal catalyst supported on a carrier; Heating the temperature while supplying a mixed gas of nitrogen gas and hydrogen gas to the reactor; And supplying a nitrogen containing compound to the reactor.

Hereinafter, the manufacturing method will be described in detail.

First, nitrogen gas is introduced in the reactor in the presence of a metal catalyst supported on a carrier.

The carrier may be selected from the group consisting of MgO, MgO, SiO ₂ , Al ₂ O ₃ , zeolites, aluminosilicates, carbon-based materials, and combinations thereof. The carbonaceous material may be natural graphite, artificial graphite, carbon black, activated carbon, activated carbon fiber, carbon nanotube, carbon nanofiber, or a combination thereof.

In addition, the metal catalyst may be a metal selected from the group consisting of Ni, Fe, Co and combinations thereof or alloys thereof. The metal catalyst may further include a metal selected from the group consisting of Mo, Cu, Cr, Pt, Ru, Pd or a combination thereof.

Next, it heats up, supplying the mixed gas of nitrogen gas and hydrogen gas to the said reactor. Hydrogen gas prevents catalyst poisoning in the catalytic chemical vapor deposition (CCVD) process and increases the synthesis yield. When the reaction proceeds under a simple mixture of hydrogen gas and a carbonizable compound, pyrolysis occurs, such as an overly fast reaction. Side reactions may occur due to the rate, and by mixing an inert gas such as nitrogen gas, a reaction rate suitable for carbon nanofiber growth by catalytic reaction may be induced.

At this time, the mixing ratio of nitrogen gas and hydrogen gas in the mixed gas is about 160: 40cc is appropriate, but is not limited thereto.

The step of raising the temperature is carried out until reaching a temperature of 300 to 700 ℃ at a temperature rising rate of 5 to 11 ℃ / min. If the temperature increase rate is slower than the above range, the synthesis time increases, which leads to a decrease in productivity. Too high a temperature causes difficulty in temperature control.

Subsequently, when the temperature reaches the desired temperature of 300 to 700 ° C., the nitrogen containing compound is fed to the reactor.

The nitrogen-containing compound may be selected from the group consisting of acetonitrile, acrylonitrile, pyrrole, pyridine and combinations thereof.

In addition, the feed rate of the nitrogen-containing compound is appropriate 0.01 ~ 0.05cc / min for a stable catalytic reaction.

Carbon nano material according to an embodiment of the present invention can be usefully used for the cathode electrode for fuel cells.

That is, the cathode electrode for a fuel cell according to another embodiment of the present invention includes the carbon nanomaterial. In general, the cathode electrode includes a cathode catalyst layer and an electrode substrate, and the carbon nanomaterial may be included in the cathode catalyst layer.

At this time, the carbon nanomaterial serves as a carrier of the catalyst causing a reduction reaction by the reaction of the oxidant, hydrogen ions and electrons supplied to the cathode electrode.

As the catalyst, for example, a platinum-based catalyst generally used as a cathode electrode catalyst of a fuel cell may be used.

The platinum-based catalyst may be platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy or platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, At least one catalyst selected from the group consisting of Cu, Zn, Sn, Mo, W, Rh and Ru). Specific examples of the platinum-based catalyst include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W , Pt / Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni and Pt / Ru / Sn / W can be used.

When using a carbon nano material according to an embodiment of the present invention as a support, and using a platinum-based catalyst on the support, the supporting process is well known in the art, so detailed description thereof will be omitted. This is easily understood by those in the field.

The cathode catalyst layer may further include a binder resin to improve adhesion of the catalyst layer and transfer of hydrogen ions.

It is preferable to use a polymer resin having hydrogen ion conductivity as the binder resin, more preferably a cation exchange group selected from the group consisting of sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphonic acid group and derivatives thereof in the side chain. Any polymer resin which has can be used. Preferably, a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer, a polyether ketone polymer, a polyether One or more hydrogen ion conductive polymers selected from ether ketone polymers or polyphenylquinoxaline polymers, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazoles [poly ( 2,2'-m-phenylene) -5,5'-bibenzimidazole] or poly (2,5-benzimidazole) may be used including one or more hydrogen ion conductive polymers.

The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in a cation exchanger at the side chain terminal. In case of replacing H with Na in the side chain terminal ion exchanger, NaOH is substituted for the preparation of the catalyst composition, and tetrabutylammonium hydroxide is substituted for tetrabutylammonium, and K, Li or Cs may be substituted with appropriate compounds. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder resin may be used in the form of a single substance or a mixture, and may also be optionally used with a nonconductive compound for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

Examples of the non-conductive compound include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), and ethylene / tetrafluoro Ethylene / tetrafluoroethylene (ETFE), ethylenechlorotrifluoro-ethylene copolymer (ECTFE), polyvinylidene fluoride, copolymer of polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), dode At least one selected from the group consisting of silbenzenesulfonic acid and sorbitol is more preferred.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant into the catalyst layer so that the oxidant can easily access the catalyst layer. The electrode substrate is a conductive substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer fiber composed of metal in a fibrous state). The metal film is formed on the surface of the formed cloth) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. Examples of the fluorine-based resin include polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride alkoxy vinyl ether, and fluorinated ethylene propylene ( Fluorinated ethylene propylene), polychlorotrifluoroethylene or copolymers thereof can be used.

In addition, a microporous layer may be further included to enhance the reactant diffusion effect in the electrode substrate. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. The binder resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, etc. may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

In the above description, the case where the carbon nanomaterial of the present invention is used as a catalyst carrier of a cathode electrode of a fuel cell has been described. have.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

* Preparation of catalyst for carbon nanofibers

An aqueous solution of iron nitride was prepared by dissolving 8.426 g of iron nitride (iron (II) nitrate, Sigma-Aldrich, Assay 98.0%) in 14.857 g of distilled water, and 7.342 g of nickel nitride (nickel nitrate, Sigma-Aldrich, Assay 99.0%). A nickel nitride aqueous solution was prepared by dissolving in 13.272 g of distilled water, and 9.935 g of magnesium nitrate hexahydrate (Junsei Chemical, Assay 97.0%) was dissolved in 9.524 g of distilled water to prepare an aqueous solution of magnesium nitride hexahydrate.

The aqueous solutions and citric acid were added to a 100 ml beaker. At this time, the amount of citric acid was used to be 0.625 times the total moles of metal contained in the aqueous solution.

Subsequently, the mixture was placed in a furnace, and then heated to 150 ° C. over 1 hour at room temperature (25 ° C.) to maintain a temperature for 10 minutes to remove moisture. The obtained product was cooled, pulverized finely, and heated up to 180 degreeC again. After holding at 180 ° C. for 2 hours, it was cooled and ground finely in mortar. The milled product was heated to 350 ° C. over 2 hours, then held at 350 ° C. for 1 hour, cooled and ground finely in a mortar to prepare a MgO ocher colored catalyst carrying NiFe catalyst. At this time, the molar ratio of Ni: Fe: MgO was 4: 1: 5.

* Nitrogen-doped carbon nanofiber fabrication

The reactor shown in FIG. 1 was prepared.

About 100 mg of the prepared MgO catalyst carrying the NiFe catalyst was prepared by spreading it evenly on an alumina plate at a width of 3 × 3 cm 2. The alumina plate prepared by evenly spreading the catalyst was placed in the center of the quartz tube of the reactor shown in FIG. 1 and then sealed using Teflon tape.

Next, the following process was carried out according to the temperature and feed gas composition profile as shown in FIG. 2.

A moisture trap was installed at the nitrogen gas outlet to remove moisture in the quartz tube and nitrogen gas.

In order to sufficiently purge the inside of the quartz tube with nitrogen at room temperature, nitrogen gas was supplied at 200 cc / min for 15 minutes.

The quartz tube was then heated to a reaction temperature (300 ° C.) for 1 hour while nitrogen gas and hydrogen gas were supplied into the quartz tube at a supply amount of 160 cc / min and 40 cc / min, respectively.

When the reaction temperature was reached, 0.035 ml / min of acetonitrile was supplied through the micropump and maintained for the reaction time. At this time, carbon nanotubes doped with nitrogen were formed.

Subsequently, the mixture was naturally cooled to room temperature while supplying nitrogen gas to the quartz tube in a supply amount of 160 cc / min. The nitrogen-doped carbon nanotubes were then collected.

The collected nitrogen-doped carbon nanotubes, 120 g of HCl, and 300 g of distilled water were mixed, and the mixture was sealed and stirred for 24 hours. HCl and distilled water were removed from the stirred product, 10% by weight of HCl was added again, followed by further stirring for 24 hours. Subsequently, the stirred product was sufficiently washed with distilled water and filtered to obtain a carbon nanotube doped with nitrogen.

(Example 2)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 340 ° C.

(Example 3)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 380 ° C.

(Example 4)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 420 ° C.

(Example 5)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 460 ° C.

(Example 6)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 500 ° C.

(Example 7)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 520 ° C.

(Example 8)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 540 ° C.

(Example 9)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the step of raising the quartz tube was performed to 600 ° C.

(Example 10)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 640 ° C.

(Example 11)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 680 ° C.

(Example 12)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 4 except that the reaction temperature was maintained at 420 ° C. for 3 hours (reaction time).

(Example 13)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 7, except that the reaction temperature was maintained at 520 ° C. for 3 hours (reaction time).

(Example 14)

Carbon nanotubes doped with nitrogen were prepared in the same manner as in Example 10 except that the reaction temperature was maintained at 640 ° C. for 3 hours (reaction time).

(Example 15)

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 10 except that the reaction temperature was maintained at 640 ° C. for 5 hours (reaction time).

(Comparative Example 1)

 The reactor shown in FIG. 1 was prepared.

About 100 mg of the prepared MgO catalyst carrying the NiFe catalyst was prepared by spreading it evenly on an alumina plate at a width of 3 × 3 cm 2.

Subsequently, the alumina plate prepared by spreading the catalyst evenly was placed in the center of the quartz tube of the reactor shown in FIG. 1 and then sealed using Teflon tape.

A moisture trap was installed at the helium gas outlet to remove moisture in the quartz tube and helium gas.

In order to sufficiently purge the inside of the quartz tube with helium gas at room temperature, helium gas was supplied at 200 cc / min for 15 minutes.

Subsequently, the quartz tube was heated to the reaction temperature (300 ° C.) for 1 hour while helium gas and hydrogen gas were supplied in a 4: 1 volume ratio into the quartz tube.

When the reaction temperature was reached, 0.035 ml / min of acetonitrile was supplied through the micropump and maintained at the reaction temperature for 1 hour (reaction time). At this time, carbon nanotubes doped with nitrogen were formed.

Subsequently, the mixture was naturally cooled to room temperature while supplying nitrogen gas to the quartz tube in a supply amount of 160 cc / min. The nitrogen-doped carbon nanotubes were then collected.

The collected nitrogen-doped carbon nanotubes, 120 g of HCl, and 300 g of distilled water were mixed, and the mixture was sealed and stirred for 24 hours. HCl and distilled water were removed from the stirred product, 10% by weight of HCl was added again, followed by further stirring for 24 hours. Subsequently, the stirred product was sufficiently washed with distilled water and filtered to obtain a carbon nanotube doped with nitrogen.

Nitrogen-doped carbon nanotubes were prepared in the same manner as in Example 1 except that the reaction temperature of the quartz tube heating step was performed up to 420 ° C.

* Synthetic yield and N / C (atomic%)

The synthesis yield of the nitrogen-doped carbon nanotubes prepared according to Examples 1 to 11 and N / C (atomic%) based on elemental analysis results are shown in FIG. 3. Synthetic yield was calculated based on TG (Thermal Gravimetry) measurement of the amount of carbon produced relative to the amount of catalyst used in the reaction process for 1 hour. In addition, elemental analysis was measured using the combustion method which analyzes each element composition ratio by quantifying the gas which arises at the time of combustion.

As shown in FIG. 3, the synthesis yield was extremely low at the reaction temperature of 300 ° C. (Example 1), while the production amount increased sharply at 340 ° C. (Example 2), and then slowly increased to the reaction temperature of 420 ° C. In addition, the synthetic yield showed a sharp decrease trend up to the reaction temperature of 520 ℃, after showing almost the same yield in the range of 520 ℃ to 650 ℃, it showed a sharp decrease trend at 680 ℃.

In addition, N / C (atomic%) tends to continuously increase from 300 deg. C (Example 1) to 520 deg. C (Example 7), slowly decreases to 650 deg. Indicated.

* SEM photo

SEM pictures of the nitrogen-doped carbon nanofibers prepared according to Examples 1 to 11 were measured and the results are shown in FIG. 4.

As shown in Fig. 4, it can be seen that the reaction temperature is not yet formed in the shape of the fiber at 340 ° C or lower .

It can be seen that the carbon nanofibers prepared according to Example 3 having a reaction temperature of 380 ° C. formed fibers having a very uniform average diameter having a size of 30 to 40 nm. In addition, it can be seen that the higher the reaction temperature, the longer the length of the fiber. When the reaction temperature is 540 ° C. or more, the fiber length distribution is similar, but as the reaction temperature increases, it can be seen that rather thick fibers having an average diameter of 70 to 100 nm appear.

* Synthetic yield according to reaction time

Synthesis yield of the carbon nanofibers prepared according to Examples 4, 7, 10 and 12 to 15 was measured and the results are shown in FIG. 5.

As shown in Figure 5, it can be seen that the synthesis amount increases as the reaction time increases at each reaction temperature.

* SEM photo

SEM photographs of the carbon nanofibers prepared according to Examples 4 and 12 are shown in FIG. 6. As shown in FIG. 6, it can be seen that the fiber length of the carbon nanofibers having a reaction time of 3 hours was longer than that of the carbon nanofibers prepared in Example 4 having a reaction time of 1 hour.

* TG measurement

For carbon nanofibers prepared according to Examples 2, 5, 7, 10 and 11, TG was measured using a TG analyzer (device: STA 409 PC, NETZSCH) under an air atmosphere. TG measurement is supplied to the TG analyzer at 30cc / min dry air, using a 10mg sample, the temperature is raised to 5K / min from room temperature to 100 ℃, and then maintained isothermal for 30 minutes at 100 ℃, After removing water | moisture content and stabilizing a state, it measured by raising the temperature of 5K / min from 100 degreeC to 900 degreeC.

The results are shown in Fig. As shown in Figure 7, it can be seen that the higher the reaction temperature, the better the oxidation resistance.

* BET measurement

Nitrogen isotherm adsorption and desorption experiments were carried out on the carbon nanofibers prepared according to Examples 1 to 11 to measure specific surface areas. Nitrogen isotherm adsorption and desorption experiments were carried out using Belsorp-II mini (Nihon Bell), pressure range p / p0 = 0 to 0.99, adsorption / desorption range. In addition, the sample was prepared by treating the prepared carbon nanofibers in a 10 wt% HCl solution for 48 hours, washed with distilled water and dried for 3 hours in a drying oven at 80 ℃. The measured specific surface area results are shown in FIG. 8. As shown in FIG. 8, the carbon nanofibers prepared according to Examples 1 to 11 had specific surface areas ranging from about 70 to 480 m 2 / g. As can be seen from FIG. 8, it can be seen that the specific surface area tends to decrease somewhat as the reaction temperature increases.

* XPS measurement

In order to observe the surface chemical properties of the carbon nanofibers prepared according to Examples 1 to 11, XPS (X-ray Photoelectron Spectroscopy) analysis was performed. In the XPS assay, the carbon, nitrogen and oxygen components were analyzed for binding samples in the range of binding energy (C: 280 to 295 eV, N: 393 sowl 410 eV, O: 520 to 540 eV). Among the results, XPS spectrum results for nitrogen of the carbon nanofibers of Examples 3 and 7 are shown in FIGS. 9 and 10. (A), (B) and (C) shown in FIGS. 9 and 10 are pyridine-like structures or pyridine-like structures nitrogen components (A) and graphite-like structures, respectively Or a pyrrole-like structure nitrogen component (B) component and a nitrogen component (C) bonded to oxygen, respectively. As a result, it can be seen that nitrogen exists in three forms of the produced carbon nanofibers.

In addition, for the carbon nanofibers prepared according to Examples 1 to 11, the total nitrogen content measured from the measured XPS results and the nitrogen content present on the carbon nanofiber surface are shown in FIG. 11. As shown in Fig. 11, the nitrogen content (about 1 to 9 atomic%) present on the surface is higher than the total nitrogen content (about 1 to 5 atomic%), and the N / C atomic ratio on the surface is the total N / C source. It can be seen that about two times higher than mercy. Since the actual catalytic reaction takes place on the surface of the catalyst and the carrier, the composition of the surface is important, and if there is more nitrogen on the surface of the total nitrogen content, the effect of nitrogen on the reaction can be seen more.

In addition, the ratio of N / C atomic ratio and said (B) component (graphite-like structure) / (A) component (pyridine-like structure) in the measured surface is shown in FIG. As shown in FIG. 12, it can be seen that as the reaction temperature increases, the graphite-like structure nitrogen component increases relatively.

* Graphitization degree analysis

In order to confirm the graphitization degree (crystallinity) of the carbon nanofibers prepared according to Examples 1 to 11, X-ray diffraction (XRD) analysis was performed. XRD analysis was performed using RINT2000 (Rigaku) and scanning speed of 0.02 per minute from 10 degrees to 80 degrees in 2θ / θ scanning mode. Among the measurement results, 2θ shows a peak corresponding to the (002) lattice plane near 26 degrees (°) in FIG. 13. As shown in Figure 13, the carbon nanofibers prepared according to Examples 1 to 11 can be seen that the peak of the (002) plane appears. In addition, it can be seen that as the reaction temperature increases, the peak central axis moves to a high angle and the width of the peak narrows, thereby increasing the crystallinity. In addition, it can be seen that as the reaction temperature increases, the 10-band is apparent.

Also, in the XRD results shown in FIG. 13, Bragg's equation (determination of interplanar distance) and Scherrer equation (determination of crystal size) were calculated from the determination parameters for the peak of (002) plane, resulting in d002 interplanar distance and Lc (002) crystal size result. Is shown in FIG. 14. As shown in FIG. 14, as the reaction temperature increases to around 500 ° C., d002 increases rapidly, and similarly above 0.341-0.343 nm at a higher temperature, Lc (002) depends on the reaction temperature. It increased almost linearly to about 2 nm at the reaction temperature of 300 ° C. and to about 6 nm at the reaction temperature of 680 ° C. As a result, it can be seen that the crystallinity of the prepared carbon nanofibers is very excellent compared to general carbon black.

* Electrochemical Characterization

A catalyst slurry was prepared by mixing 20 mg of carbon nanofibers prepared according to Examples 4, 7 and 10, 40 μl of a 10 wt% Nafion solution (water solvent, Dupont), 40 μl of distilled water, and 1 g of ethanol. The catalyst slurry was applied to 10 µl of glass carbon having a 1 cm 2 area and dried to prepare a working electrode.

Instead of the carbon nanotubes prepared in Example 2 in Comparative Example 2, working electrodes were prepared in the same manner as described above using carbon black (Cabot Vulcan XC72R).

A working electrode was prepared in the same manner as described above using plate-type CNF (Ssuntel RP-610: CNF1) instead of the carbon nanotubes prepared in Example 3 in Comparative Example 3.

A working electrode was prepared in the same manner as described above using carbon nanofibers (CNF 2) synthesized at 520 ° C. using ethylene as a carbon source instead of the carbon nanotubes prepared in Example 4 as a comparative example.

Electrochemical experiments were conducted with a three-electrode system using the prepared working electrode, a counter electrode platinum mesh and Ag / AgCl (ALS. RE-1B, standard hydrogen electrode: NHE) as reference electrode.

Electrochemical experiments were carried out in a 0.1 M HClO ₄ aqueous solution sufficiently purged with nitrogen gas, at 0.0 to 1.2 V based on the NHE electrode, and oxygen reduction reaction (ORR) experiment was sufficiently purged with oxygen. In a 0.1 M HClO ₄ aqueous solution was carried out at 1.2 to 0.2V based on the NHE electrode. In addition, the potential sweep rate was fixed at 20 mV / sec.

The results of the cyclic voltametry experiment are shown in FIG. 15, and the results of the ORR experiment are shown in FIG. 16.

As shown in FIG. 15, Examples 4, 7 and 10, and Comparative Examples 2-4, all carbon materials exhibit a rectangular pattern by typical electrical double layer formation, but the carbon nanofibers of Examples 4, 7 and 10 When used, it can be seen that the internal area is large. As such, a large internal area indicates a large amount of ion adsorption, which means that the ion adsorption capacity is excellent, and as a result, it can be predicted that the catalyst supporting properties and the interaction between the catalyst and the carrier will be excellent when used as a catalyst carrier for fuel cells. have.

In addition, as shown in Figure 16, the carbon nanofibers of Examples 4, 7 and 10 has an oxygen reduction activity, it can be seen that the carbon material of Comparative Examples 2 to 4 does not have an oxygen reduction activity. From this result, it can be seen that the carbon nanofibers of Examples 4, 7 and 10 can be used as catalysts on the cathode electrode by themselves.

(Example 16)

A catalyst precursor solution was prepared by stirring a platinum precursor (Chloroplatinic acid hydride 99.9%, Aldrich), a carbon nanofiber carrier prepared according to Example 11, and 400 ml of distilled water for 48 hours.

NaBH ₄ was prepared by dissolving it in 400 ml of distilled water in an amount of 15 times the molar ratio of the metal to be supported, and stirred sufficiently for 30 minutes, and then stirred for 48 hours to prepare a NaBH ₄ solution. The catalyst precursor solution was added to the NaBH ₄ solution and stirred for 1 hour to reduce. The reduced product was washed with 1 L of distilled water and filtered, and dried in an oven at 80 ° C. for about 2 hours to prepare a Pt / carbon nanofiber catalyst (Pt / N640).

(Example 17)

Platinum precursor (Chloroplatinic acid hydride 99.9%, Aldrich), the carbon nanofiber carrier prepared according to Example 13 and 400ml of distilled water was stirred for 48 hours, except that the catalyst precursor solution was prepared in the same manner as in Example 16 above. The Pt / carbon nano fiber catalyst (Pt / N523) was produced.

(Example 18)

Catalyst precursor by stirring platinum precursor (Chloroplatinic acid hydride 99.9%, Aldrich), palladium precursor (Palladium (II) chloride 99.9%, Sigma-Aldrich), carbon nanofiber carrier prepared according to Example 13 and 400 ml of distilled water for 48 hours A PtPd / carbon nanofiber catalyst (PtPd / N523) was prepared in the same manner as in Example 16 except that the solution was prepared. At this time, the weight ratio of platinum and palladium is 1: 2:

(Comparative Example 5)

Pt / carbon nanofibers were prepared in the same manner as in Example 16, except that the catalyst precursor solution was prepared by stirring the platinum precursor (Chloroplatinic acid hydride 99.9%, Aldrich), the carbon black carrier, and 400 ml of distilled water for 48 hours. Catalyst (Pt / CB) was prepared.

(Comparative Example 6)

A commercially available platinum-palladium catalyst (JM9000, Johnson Matthey Fuel Cells-Hipec Series) was used. At this time, the weight ratio of platinum and palladium is 1: 2:

A catalyst slurry was prepared by mixing 20 mg of the catalyst prepared according to Examples 16 to 18 and Comparative Examples 5 to 6, 40 µl of Nafion solution (water solvent, Dupont), 40 µl of distilled water, and 1 g of ethanol. . 10 microliters of this catalyst slurry were apply | coated to glass carbon, and it fully dried, and prepared the electrode.

Using the prepared electrode, using H ₂ SO ₄ as the electrolyte was carried out in the same manner as the cyclic voltametry experiment and the oxygen reduction reaction experiment to obtain a cyclic voltametry experiment and oxygen reduction reaction experiment results. The results are shown in FIGS. 17 and 18, respectively. The cyclic voltammetry test results shown in FIG. 17 are the values at five cycles, and Comparative Example 6 showed the highest value for the electrochemical surface area (ECSA) of the catalyst according to the amount of hydrogen desorption. , Example 18 showed similar results as in Comparative Example 6.

In addition, as shown in FIG. 18, it can be seen that the catalysts of Comparative Examples 5 and 16 are excellent in activity.

Claims (18)

Carbon nanomaterials comprising carbon nanofibers comprising nitrogen. The method of claim 1,
The nitrogen is a carbon nano material that is doped with carbon nano fibers. The method of claim 1,
In the carbon nanofibers, the nitrogen content is 0.5 to 10 atomic% carbon nano material. The method of claim 1,
Carbon nano material of the carbon nanofibers in the ratio of nitrogen to carbon (N / C) is 1.0 to 5.0 atomic%. The method of claim 1,
Wherein the carbon nanofibers have a herringbone structure. The method of claim 1,
Carbon nano material is an average diameter of the carbon nanofiber is 30 to 100nm. The method of claim 1,
Wherein the carbon nanofibers have a specific surface area of 50 to 500 m ² / g. The method of claim 1,
The carbon nanofibers are carbon nanomaterials having a (002) plane peak at 20 to 30 ° when 2θ is measured by X-ray diffraction measurement using CuKα. Introducing nitrogen gas in the reactor in the presence of a metal catalyst supported on a carrier;
Heating the temperature while supplying a mixed gas of nitrogen gas and hydrogen gas to the reactor; And
Supplying a nitrogen-containing compound to the reactor
Method of producing a carbon nano material comprising a. 10. The method of claim 9,
Wherein the carrier is selected from the group consisting of MgO, SiO ₂ , Al ₂ O ₃ , zeolites, aluminosilicates, carbon-based materials, and combinations thereof. 10. The method of claim 9,
The metal catalyst is a method of producing a carbon nano material is a metal selected from the group consisting of Ni, Fe, Co and combinations thereof or alloys thereof. 10. The method of claim 9,
The mixing ratio of nitrogen gas and hydrogen gas in the mixed gas is 160: 40 cc method of producing a carbon nano material. 10. The method of claim 9,
The supply amount of the mixed gas is 200 cc / min method for producing a carbon nano material. 10. The method of claim 9,
The step of raising the temperature is carried out until the temperature of 300 to 700 ℃ at a temperature increase rate of 5 to 11 ℃ / min is carried out. 10. The method of claim 9,
The nitrogen-containing compound is selected from the group consisting of acetonitrile, acrylonitrile, pyrrole, pyridine and combinations thereof. 10. The method of claim 9,
And a feed rate of the nitrogen-containing compound is 0.035 cc / min. The method of claim 7, wherein
Supplying the nitrogen-containing compound is a method of producing a carbon nano material is carried out at a temperature of 300 to 700 ℃. A catalyst comprising the carbon nano material according to any one of claims 1 to 8 as a support.

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