WO2016043396A1 - Method for preparing nitrogen-doped graphene and nitrogen-doped graphene prepared thereby - Google Patents

Abstract

The present invention relates to a method for preparing nitrogen-doped graphene, the method comprising: a first step for preparing a mixed solution containing carbon atoms and nitrogen atoms by putting a carbon compound and an amine compound into an acidic solution, followed by heating, stirring, and thermal decomposition; a second step for forming a compound containing carbon atoms, nitrogen atoms, and Fe²⁺, and then obtaining the compound, the compound being formed by adding an Fe²⁺-containing solution to the mixed solution containing carbon atoms and nitrogen atoms, followed by stirring; a third step for forming an Fe substrate by thermally treating the compound, which is obtained in the second step, under a nitrogen ambience; and a fourth step for forming nitrogen-doped graphene by, after the third step, diffusing the carbon atoms and the nitrogen atoms, which are contained in the compound, into the Fe substrate through cooling. More preferably, the method further comprises a fifth step for removing, after the fourth step, the Fe substrate by adding an acid to cause a reaction.

Description

Process for preparing nitrogen doped graphene and nitrogen doped graphene prepared therefrom

The present invention relates to a method of preparing nitrogen-doped graphene, wherein carbon and nitrogen are supplied from a carbon compound and an amine compound, and Fe ²⁺ ions are used as graphene growth catalysts to control the content of pyridine-like arrays. The present invention relates to a method for preparing nitrogen doped graphene, which has an improved content of nitrogen and shows excellent electrochemical activity for redox reactions.

Graphene is a hexagonal two-dimensional monolayer composed of carbon atoms. It is a 0-dimensional fullerene, a tube-shaped one-dimensional structure of carbon nanotubes, and 3 Due to the structural difference from graphite having a dimensional structure, graphene has excellent electrical, mechanical, and chemical properties, and has excellent conductivity. In other words, since graphene has a 2-dimensional ballistic transport property, the mobility of charge in graphene is very high, and thus the charge mobility of 15,000 cm ² V ^-1 s ^-1 or higher is maintained at room temperature. see.

In addition, graphene has the advantage that it is very easy to process one-dimensional, two-dimensional nanopatterns made of carbon, which is a relatively light element, and it is possible to control semiconductor-conductor properties as well as the chemical bonding of carbon. The diversity also enables the manufacture of a wide range of functional devices, including sensors and memories.

In order to apply graphene to the above-mentioned various functional devices, a doping process that can improve electrical characteristics such as sheet resistance and charge mobility of graphene is essential.

As a result, the nitrogen-doped graphene has a high surface area, excellent electrical conductivity, and a conjugation of the π-optal of graphene with the lone pair of nitrogen.

Methods for preparing graphene doped with nitrogen generally fall into three categories.

Chemical vapor deposition (CVD) is a method in which gaseous components react chemically to form a graphene thin film on the surface of a substrate on which a specific metal is deposited. It is carried out under nitrogen urea and is the most common method of in situ doping with nitrogen. This manufacturing method provides relatively low defects of graphene, but the process temperature must be maintained at a high temperature in order to supply the raw materials of graphene to be manufactured in gaseous form. There is a need for a process that is only possible on metal-deposited surfaces and that the grown graphene must be transferred back to the desired substrate. In addition, it is difficult to grow the size by growing graphene.

In the case of the nitrogen plasma method, graphene is placed in an electric furnace and nitrogen is put into a plasma state at a high temperature to replace graphene carbon with nitrogen. Such a post-doping method may be used in addition to the nitrogen plasma method. There is a method of bonding nitrogen atoms to the graphene lattice by thermal annealing of graphene and ammonia, arc-discharge of graphene and pyridine / ammonia, and high power electrical annealing of graphene and ammonia. These methods can obtain high purity graphene but often have a low nitrogen content in the prepared nitrogen-doped graphene, which does not have surface properties due to nitrogen doping, which may affect the catalytic activity of the redox reaction. There is also a problem.

In addition, nitrogen-doped carbon materials may be prepared through thermal decomposition of transition metal macrocyclic compounds, but these compounds are expensive or difficult to synthesize.

In the present invention, in order to solve the above problems, by using a carbon compound and an amine compound as a source of carbon and nitrogen, and Fe ^{2 +} ions as a graphene growth catalyst, while controlling the content of the pyridine-like arrangement It is an object of the present invention to provide a method for preparing nitrogen-doped graphene, in which the content of nitrogen is improved to exhibit excellent electrochemical activity for redox reactions.

In another aspect, the present invention provides a nitrogen-doped graphene prepared by the above method as another problem.

In addition, another object of the present invention is to provide an electrochemical energy device containing the nitrogen-doped graphene.

According to an aspect of the present invention for solving the above problems,

A first step of preparing a mixture solution containing carbon atoms and nitrogen atoms by adding a carbon compound and an amine compound to an acidic solution, followed by heating and stirring to pyrolyze;

A second step of forming a compound including carbon atoms, nitrogen atoms and Fe ²⁺ ions by adding and stirring a solution containing Fe ²⁺ ions to the mixture solution containing carbon atoms and nitrogen atoms, and then obtaining them ;

A third step of forming a Fe substrate by heat-treating the compound obtained in the second step in a nitrogen atmosphere; And

After the third step, by cooling the carbon atoms and nitrogen atoms contained in the compound comprising a fourth step of forming a nitrogen-doped graphene by diffusing on the Fe substrate, of the nitrogen-doped graphene A manufacturing method is provided.

In addition, in order to solve another object of the present invention, there is provided a nitrogen doped graphene prepared by the above method.

According to the nitrogen-doped graphene manufacturing method of the present invention, carbon and nitrogen for the production of nitrogen-doped graphene from a carbon compound and an amine compound are supplied, in particular by using melamine as a nitrogen source, It is possible to improve the content of nitrogen, and furthermore, to control the content of the pyridine-like arrangement shows excellent electrochemical activity for the Oxygen Reduction Reaction (ORR).

In addition, as the added Fe ²⁺ ions function as growth catalysts for growing nitrogen-doped graphene and are formed as Fe substrates during the entire process of forming nitrogen-doped graphene, the nitrogen atoms to be doped By stabilizing them, it is possible to overcome the limitations of the substrate surface to form nitrogen-doped multilayered graphene and increase the size of the graphene.

In addition, as the present invention suggests that the multilayered graphene can be prepared as a protein or a carbohydrate, it can be widely used in the field of electrochemical energy devices.

1 is a schematic view showing a method for preparing a nitrogen doped multilayer graphene according to the present invention.

Figure 2 shows (a) TEM image, (b) AFM image, (c) XPS graph, (d) Raman spectrum of N-MLG-45min according to an embodiment of the present invention.

3 shows an XPS graph according to an embodiment of the present invention. (A) XPS graph for nitrogen of N-MLG-45min, (b) XPS graph for nitrogen of N-MLG-45min, N-MLG-90min, N-MLG-120min)

Figure 4 shows the Raman spectrum of N-MLG-45min, N-MLG-90min, N-MLG-120min of the present invention.

Figure 5 is a linear scan voltage-current curve according to an embodiment of the present invention, (b) rotating disk voltage-current curve, (c) Koutecky-Levich graph, (d) the linear scan voltage according to the Fe content -Shows the current curve.

6 shows TGA curves according to Examples 1 to 3 of the present invention.

Hereinafter, the present invention will be described in more detail. Details that are not described in the specification of the present invention can be sufficiently recognized and inferred by those skilled in the art or similar fields of the present invention, so description thereof is omitted. In addition, specific details of the embodiments are included in the detailed description and drawings, the present invention is not limited to the embodiments disclosed below.

The present invention relates to a method for preparing nitrogen-doped graphene capable of improving nitrogen content and growing graphene, according to an aspect of the present invention.

A first step of preparing a mixture solution containing carbon atoms and nitrogen atoms by adding a carbon compound and an amine compound to an acidic solution, followed by heating and stirring to pyrolyze;

A second step of forming a compound including carbon atoms, nitrogen atoms and Fe ²⁺ ions by adding and stirring a solution containing Fe ²⁺ ions to the mixture solution containing carbon atoms and nitrogen atoms, and then obtaining them ;

A third step of forming a Fe substrate by heat-treating the compound obtained in the second step in a nitrogen atmosphere; And

After the third step, by cooling to provide a nitrogen-doped graphene comprising a fourth step of forming a nitrogen-doped graphene by diffusing carbon atoms and nitrogen atoms contained in the compound on the Fe substrate A method is provided.

First, the first step is to prepare a mixture solution containing carbon atoms and nitrogen atoms by adding a carbon compound and an amine compound to an acidic solution and heating and stirring to decompose the carbon compound, wherein the carbon compound is a protein, a monosaccharide, a disaccharide, an oligosaccharide. It is characterized in that any one selected from the group consisting of polysaccharides and combinations thereof, more preferably characterized in that the protein is a milk protein.

In addition, the amine compound is melamine (C ₃ H ₆ N ₆ ), ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), pyridine (C ₅ H ₅ N), pyrrole (C ₄ H ₅ N), acetonitrile (CH ₃ CN), triethanolamine (C ₆ H ₁₅ NO ₃ ), aniline (C ₆ H ₇ N) 3-aminobenzoic acid (C ₇ H ₇ NO ₂ ), 4-aminobenzoic acid, 3- (4-aminophenyl ) Benzoic acid (C ₁₃ H ₁₁ NO ₂ ), 4- (4-aminophenyl) benzoic acid, 4- (3-aminophenyl) benzoic acid (C ₁₃ H ₁₁ NO ₂ ), 5-aminoisophthalic acid (C ₈ H ₇ NO ₄ ), 3- (4-aminophenoxy) benzoic acid (C ₁₃ H ₁₁ NO ₃ ), 4- (4-aminophenoxy) benzoic acid, 3,4-diaminobenzoic acid (C ₇ H ₈ N ₂ O ₂ ) , 3,5-diaminobenzoic acid, 3-aminobenzoamide (C ₇ H ₈ N ₂ O), 4-aminobenzoamide and any one compound selected from the group consisting of a combination thereof, Preferably, the amine compound is characterized in that the melamine.

More specifically, in the first step of the present invention, as the pyrolysis of the carbon compound and the amine compound into a mixture containing carbon atoms and nitrogen atoms, the base on which the Fe ²⁺ ions to be added in the second step can be stirred In the production of graphene of the present invention, a protein and a carbohydrate (a group consisting of monosaccharides, disaccharides, oligosaccharides, polysaccharides, and combinations thereof) are used as a carbon compound as a carbon source. Since this can be applied in the field of electrical energy devices, the protein and carbohydrates become a promising carbon source that can be widely applied in the field of electrical energy devices.

In addition, when using the amine compound melamine as a nitrogen source as described above, it is possible to form a nitrogen-doped multilayered graphene, which significantly improves the nitrogen content in the preparation of the nitrogen-doped graphene. In one embodiment of the present invention to prepare a nitrogen doped multilayer graphene having a nitrogen content of 7.41%.

In addition, by using a protein including an amine group among carbon compounds used as a carbon source of nitrogen doped graphene, it can also be used as a source of nitrogen doped.

Next, in the second step, after adding a solution containing Fe ²⁺ ions to the mixture solution containing the carbon atom and the nitrogen atom, the mixture is stirred to form a compound including the carbon atom, the nitrogen atom, and the Fe ²⁺ ion. In a step of obtaining the same, the mixture solution containing the carbon atom and the nitrogen atom and the solution containing Fe ²⁺ ions are stirred under nitrogen protection.

In more detail, the solution containing Fe ²⁺ ions is a solution further comprising an ammonium group, and supplies Fe ²⁺ ions to a mixture solution containing carbon and nitrogen atoms formed in the first step, as well as being doped. It can be a source of nitrogen atoms.

In addition, by adding a small amount of Fe when supplying the Fe ²⁺ ions, the added amount of Fe does not participate in the reaction, but prevents Fe ²⁺ ions from being oxidized to Fe ³⁺ ions.

The third step is to form a Fe substrate by heat-treating the compound obtained in the second step in a nitrogen atmosphere, in detail, the heat treatment of the third step is 850 ~ 1200 ℃ under nitrogen atmosphere for 45-120 minutes In particular, as the reaction is carried out for 45 to 90 minutes under the heat treatment conditions, the nitrogen content of the nitrogen-doped graphene is improved, and the multilayer nitrogen graphene formed forms a pyridine-like array 30. It includes ˜35% to improve the function as a catalyst of the redox reaction.

In addition, the Fe substrate formed in the third step is similar to the function of the substrate in the CVD manufacturing method, but unlike the CVD manufacturing method, the Fe substrate of the present invention is formed during the entire process of forming the nitrogen-doped graphene Fe ²⁺ ions contribute to the stabilization of the nitrogen atoms doped together with the function as a growth catalyst to grow nitrogen doped graphene. That is, the size of nitrogen doped multilayer graphene can be grown by overcoming the limitation of the limited substrate surface, including nitrogen doped monolayer graphene and nitrogen doped multilayer graphene.

Further, as the heat treatment reaction of the third step is carried out in a nitrogen atmosphere, it can be used also as a source of nitrogen to be doped.

Finally, the fourth step is a step of forming a nitrogen-doped graphene by diffusing carbon atoms and nitrogen atoms included in the compound on the Fe substrate by cooling after the third step.

In this case, the nitrogen-doped graphene is characterized in that the nitrogen-doped multilayer graphene.

In addition, in the nitrogen-doped graphene formed according to the present invention, the doped nitrogen is composed of pyridinic-N, pyrrolic-N, and graphite-N, graphitic-N. Pyridine-like arrangements contain 30-35%.

In addition, the source of the doped nitrogen atoms, in addition to the amine compound, nitrogen according to the nitrogen atmosphere formed during the nitrogen-doped graphene production reaction, the Fe ²⁺ ion solution nitrogen further comprising an ammonium group added in the second step In addition, there is nitrogen contained in the protein which is the carbon compound of the first step, and the amine compound is more preferably melamine.

The nitrogen-doped graphene manufacturing method of the present invention may further include a fifth step of removing the Fe substrate by reacting by adding an acid after the last fourth step.

In the present invention, since Fe has a catalytic role of growing graphene and a function of stabilizing doped nitrogen, but does not have a catalytic function for redox reaction, the Fe substrate prepared in the fourth step is not removed. In the case of doped graphene, the redox reaction is similar to that of the nitrogen doped graphene from which the Fe substrate prepared by further including the fifth step is removed, but the activity of the redox reaction is reduced. .

Therefore, it is more preferable to manufacture the nitrogen-doped graphene from which the Fe substrate is removed by further including the fifth step.

According to another aspect of the present invention, there is provided a nitrogen doped graphene, characterized in that produced by the above-described method.

Further, according to another aspect, the present invention provides an electrochemical energy device containing the prepared nitrogen doped graphene.

Preferably, the electrochemical energy device containing nitrogen-doped graphene includes a fuel cell and metal-air-batteries.

In the following examples and analysis will be described with reference to the drawings, as described above, the present invention is not limited to the embodiments disclosed below.

<Example>

Preparation of Nitrogen Doped Multilayer Graphene

18.1 g of milk powder and 1.9 g of melamine were added to HCl solution (6.0 mol / L, 500 ml), stirred at 107 ° C. for 24 hours, cooled and filtered under reduced pressure. And 10% NaOH solution was added until the pH of the mixture solution approached 5.0 and buffered.

To the mixture solution was added Fe (NH ₄ ) ₂ (SO ₄ ) ₂ (1.0 mol / L, 200 mL) containing excess 100 mg Fe, and then some citric acid buffer (0.1 mol / L) was added to the mixture solution. Was added until the pH was close to 6.5. Thereafter, the mixture was stirred at room temperature under a nitrogen atmosphere for 12 hours, and finally the solid was separated by centrifugation, which was repeated three times so that sufficient Fe ²⁺ ions could be added to the mixture (two times). Cycles of centrifugation and washing with water).

The solid obtained as above was dried in vacuo and then heat treated at 1000 ° C. under a nitrogen atmosphere.

Thereafter, a nitrogen-doped multilayer graphene soot was prepared by treatment with HCl (2.0 mol / L, 200 mL) at 80 ° C.

The prepared nitrogen-doped multilayer graphene soot is dispersed in water by centrifugation, and the upper centrifuge is obtained through filtration, washing, and drying, so that about 2 g of nitrogen-doped multilayer graphene is obtained. Obtained.

The manufacturing process of the nitrogen doped multilayer graphene according to the present embodiment is shown in FIG.

Preparation of Nitrogen Doped Multilayer Graphene According to Heat Treatment Time

In the preparation of the nitrogen-doped multilayered graphene, to obtain a compound containing Fe ²⁺ ions in order to prepare the Fe substrate, the reaction was heat-treated at 1000 ° C. under nitrogen atmosphere for 45 minutes, 90 minutes, and 120 minutes, respectively. Leveling was at N-MLG-45min, N-MLG-90min, N-MLG-120min. However, the samples were treated with HCl at 80 ° C. for 6 hours after the Fe substrate was prepared to remove the Fe substrate.

Table 1

	N-MLG-45min	N-MLG-90min	N-MLG-120min
Fe substrate manufacturing step Heat treatment (1000 ℃) Reaction time (min)	45	90	120

Preparation of Nitrogen Doped Multilayer Graphene According to Fe Content

In the preparation of the nitrogen-doped multilayered graphene, a heat treatment reaction for producing Fe substrates was performed for 45 minutes, 60 minutes, and 90 minutes, and treated with 0 h, 3 h, and 6 h with HCl at 80 ° C. to remove Fe. Nitrogen doped multilayer graphene having different Fe contents was prepared, and the conditions are shown in Table 2 below.

TABLE 2

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7
Fe substrate manufacturing step Heat treatment (1000 ℃) Reaction time (min)	45			60		90
Fe removal reaction (HCl treatment time)	0	3	6	0	6	0	6

<Characteristic analysis>

Analysis method

Transmission Electron Microscopy (TEM) images were measured using a high-resolution JEOL 2000F TEM system operating on LaB6 filaments at 2000 kV.

Atomic force microscopy (AFM) images were measured using a Nanonavi Probe Station and Seiko SPA 400 in tapping mode.

X-ray Photoelectron Spectroscopy (XPS), ESCALAB250 from VG Scientific Ltd, was used to measure the valence electron state and binding energy of the samples prepared from the above examples, and graphene surface materials were selected.

Raman spectra were measured using a micro-Raman spectrometer (Renishaw, InVia). The laser beam excited at the 514 nm wavelength was focused by the objective lens, with a numerical aperture of 0.75 on the sample about 1 탆 ² .

TGA was measured using a Pyris Diamon TG / DTA thermogravimetric analyzer from Perkin-Elmer. The sample was measured by heating to 10 ° C. min ⁻¹ from room temperature to 900 ° C. in air.

Measurement of electrochemical properties was carried out using a three-electrode test cell at room temperature using potentiostat CHI 660D. Glassy carbon electrodes (GCE), Pt gauze and Hg / HgO / KOH (1.0 M) were used as working electrodes, auxiliary electrodes and reference electrodes, respectively.

In addition, the polarization curve for the redox reaction was measured using a Rotating Disc Electrodes (RDE) while controlling the speed with Metrohm 628-10unit in 1.0M KOH solution.

Confirmation of Formation of Nitrogen Doped Multilayer Graphene (N-MLG-45min)

Figure 2 shows the (a) TEM image, (b) AFM image, (c) XPS graph, (d) Raman spectrum for N-MLG-45min, through which the nitrogen doped multilayer graphene was formed. there was.

That is, FIG. 2 (a) nitrogen-doped multilayer yes from a TEM image of a pin 1㎛ is present in a large area of ² or more, Fig. 2 (b) through an AFM image of 800nm ~ 2㎛ side size and a thickness of about 1.7nm It can be seen that it consists of at least 10 layers of graphene, and through the XPS graph of FIG. 2 (c), as the surface material of the nitrogen-doped multilayer graphene is represented by carbon, nitrogen, and oxygen, It was found that the Fe atom only promotes the growth of graphene but is not a component. In addition, it can be seen that as the Raman spectrum of FIG. 2 (d) shows G-band, D-band, and 2D-band, graphene doped with nitrogen was formed.

XPS Analysis

Figure 3 (a) is an XPS graph for N (N) of N-MLG-45min, Figure 3 (b) is a nitrogen for N-MLG-45min, N-MLG-90min, N-MLG-120min respectively The XPS graph is shown, through which the doped nitrogen type and its intensity and binding energy can be analyzed, and these data are summarized in Table 3 below.

 N1 is a pyridinic-N with pyridine-like arrangement, N2 is a pyrrolic-N with pyrrole-like arrangement, and N3 represents a nitrogen-like graphitic-N with graphite-like arrangement. .

TABLE 3

sample	Total nitrogen (N) content (at.%)	XPS Analysis (%)			Binding energy (eV)
	N	N1	N2	N3	N1	N2	N3
N-MLG-45min	7.41	34.6	30.6	34.8	398.7	400.3	402.0
N-MLG-90min	6.13	30.4	29.9	39.7
N-MLG-120min	3.45	24.8	30.1	45.1

Referring to Table 3, the nitrogen doped multilayer graphene of the present invention comprises three types of nitrogen doping, N1 (pyridinic-N), N2 (pyrrolic-N), N3 (graphitic-N), nitrogen-doped multilayer In graphene, the total nitrogen content percentage including the three types of nitrogen doping decreases from 7.41% to 3.45% as the heat treatment time increases. It is believed that some nitrogen atoms are separated from the carbon plane as the heat treatment time increases.

More specifically, each of the three types of nitrogen with respect to the total doped nitrogen content, as the heat treatment reaction time increases, hardly changes the case of N2 (pyrrolic-N), but the content of N1 (pyridinic-N) From 34.6% to 24.8%, N3 (graphitic-N) content was found to increase from 34.8% to 45.1%. It is believed that pyridinic-N (N1) nitrogen type is changed to N3 (graphitic-N) as the heat treatment time increases at high temperature (1000 ° C).

In addition, the binding energy of each doped nitrogen type was found to be the lowest as 398.7eV when N1 (pyridinic-N), 402.0eV when the N3 (graphitic-N). In the case of the N1 (pyridinic-N) nitrogen type, the nitrogen atom binds two carbon atoms and gives the π-electron, the lone pair, as an aromatic π system, while in the N3 (graphitic-N) nitrogen type, the nitrogen atom has three nitrogen atoms. The binding force of the N3 nitrogen type was higher because the bonding energy of the N3 nitrogen type was higher than that of the N1 nitrogen type because it is bonded to the carbon atom and there is no lone pair around the nitrogen atom.

Raman Spectrum Analysis

In preparing nitrogen-doped multilayered graphene, Raman spectrum analysis was performed on N-MLG-45 min, N-MLG-90 min, and N-MLG-120 min. This is shown in FIG.

Referring to FIG. 4, as the heat treatment time increases from 45 minutes to 90 minutes, the nitrogen type (pyridinic-N) having a pyridine-like arrangement decreases and the nitrogen type (graphitic-N) having a graphite-like arrangement increases. As the heat treatment time was increased, it was determined that pyridine pseudo-array nitrogen (pyridinic-N) was converted into graphite pseudo-array nitrogen (graphitic-N), and thus the value of I _G / I _D was increased.

In addition, as the heat treatment time increased further from 90 minutes to 120 minutes, the nitrogen atoms were removed from the carbon plane, thus reducing the nitrogen content in the nitrogen doped multilayer graphene and increasing the defects on the carbon plane. The value of _G / I _D is reduced.

In addition, through the G-band line shown in red in Figure 4, it can be seen that as the heating time increases, the content of graphite pseudo-array nitrogen (graphitic-N) increases.

The results are consistent with the XPS graph of FIG. 3, which means that pyridin-like nitrogen (pyridinic-N) can be converted into graphite-like nitrogen (graphitic-N) as the heat treatment time increases.

Electrochemical Catalytic Activity Analysis

1) Linear Sweep Voltammetry

FIG. 5 (a) contains N-MLG-45min, N-MLG-90min, N-MLG-120min, CNTs, undoped graphene and 20wt% Pt in oxygen saturated 1.0 M KOH solution The linear sweep voltammetry of Pt / C is shown. In FIG. 5 (a), the starting potential of N-MLG-45min is -0.05V, and the CNTs starting potential is -0.25V. The graphene (graphene) starting potential was found to be high compared to -0.24V. This proves that the carbon atoms adjacent to the nitrogen dopant have a significant amount of charge density to offset the strong electron affinity of the nitrogen atoms, which is characterized by O ₂ and It is shown that the reaction intermediate has improved adsorbability, thereby improving the redox reaction. In addition, nitrogen-induced charge delocalization can change the chemisorption mode of O ₂ from being adsorbed at the end of the undoped carbon monoatomic side to the diatomic side on the nitrogen doped carbon. It is possible to effectively weaken the oxygen-oxygen bond in order to promote the redox reaction.

However, the starting potential of N-MLG-45min (-0.05V) is slightly lower than the starting potential of Pt / C catalyst (0.01V), but is higher than most catalyst starting potentials not based on Pt, and moreover, N-MLG- The current density of 45 min was similar to that of the Pt / C catalyst.

In addition, looking at N-MLG-45min, N-MLG-90min, which is nitrogen-doped multilayer graphene in Figure 5 (a), the total nitrogen content of each is similar to 7.41%, 6.13%, but N-MLG-45min The half-wave potential of -0.18V was higher than that of N-MLG-90min, compared to -0.23V. Through this, the half-wave potential value of N-MLG-45min is higher than N-MLG-90min is the difference in the type of the doped nitrogen, that is, the content of the pyridine pseudo-array nitrogen (pyridinic-N), pyridine pseudo-array nitrogen (pyridinic-N) is believed to improve the electrocatalytic performance of the redox reaction.

In other words, the electrocatalytic activity of nitrogen doped multilayer graphene was found to be directly related to the nitrogen content and the ratio of pyridinic-array nitrogen (pyridinic-N) to the total doped nitrogen.

2) Linear Scanning Voltage-Current Curve Analysis Using Rotating Disc Electrode (RDE)

Figure 5 (b) shows a linear scan voltage-current curve using a rotating disk electrode, the voltage for N-MLG-45min with different rotational speed using the rotating disk electrode in 1.0M KOH solution saturated with O ₂ -Shows the current curve.

Rotating Disc Electrodes (RDE) data were analyzed using Koutecky-Levich equation.

However, when the current density J is measured in the above, J _K and J _L are kinetic current density and diffusion limit current density, respectively.

Is the rotational speed of the rotating disc electrode, n is the number of electrons transferred, F is the Faraday constant (96485Cmol ^-1 ),

Is the bulk concentration of O ₂ dissolved in the electrolyte,

Is the O ₂ diffusion coefficient,

Is the kinematic viscosity of the electrolyte.

Figure 5 (c) is the inverse of the current density of the electrochemical oxygen reduction process for N-MLG-45min J- ¹

As a Koutecky-Levich linear graph for, it is possible to obtain the values of J _K and B from the y-intercept and the slope of the linear graph.

= 0.93 × 10 ^-6 molcm ^-3 ,

= 1.30 × 10 ^-5 cm ² s ^-1 ,

= 5.45 × 10 ⁻³ cm ² s ⁻¹ .

As shown in FIG. 5 (b), the voltage-current was measured under various RDE rpms (800, 1200, 1600, 2000 rpm) to obtain n values through J _K and B values in FIG. 5 (c). The current remains almost constant in the potential range of 0.090V to 0.20V.

Accordingly, in FIG. 5 (c), a constant value of the electron potential for the redox reaction is shown at different electrode potentials of −0.2 V, −0.25 V, and 0.40 V. FIG.

In other words, the number n of electrons transferred through Koutecky-Levich equations (1) to (3) is measured to be about 4, which is the target product H ₂ O directly without passing through H ₂ O ₂ as an intermediate in the reduction reaction of oxygen. The reaction proceeds to obtain a total of four electron transfer means. This can be confirmed through the following schemes (4) to (8).

In the above reaction schemes (4) to (8), it is described that the oxygen reduction proceeds by transferring four electrons in the oxygen reduction for N-MLG-45min, the oxygen molecules are graphene in an aqueous solvent as shown in Equation (4) After being adsorbed on the sheet, four electrons are transferred as shown in Equations (5) to (8), thereby forming nitrogen-doped multilayer graphene (N-MLG) and H ₂ O.

That is, four electrons are transferred from the reaction mechanism to form nitrogen-doped multilayered graphene (N-MLG) and H ₂ O, but do not include hydrogen peroxide and have high Faraday efficiency, thereby increasing redox reaction efficiency.

3) Catalyst (Fe) activity analysis

Catalyst (Fe) activity was analyzed to the extent of oxidation according to the Fe content.

5d and 6 show linear scan voltage-current graphs and TGA curves according to Fe content for Examples 1 to 3 (heat treatment time 45 minutes, HCl treatment time 0, 3, 6h), respectively.

Referring to the linear scan voltage-current graph of FIG. 5D, Example 1 (0h) without Fe removal, Example 2 (3h) with reduced Fe content, and Example 3 (6h) with Fe removed are similar half-waves. With the potential, Example 1 (0h), which has similar functionality in the redox reaction but is high in Fe content, caused a reduction in redox activity.

That is, Fe contributes to the function of the growth catalyst for growing graphene and the stabilization of the doped nitrogen, but it does not seem to have a functional in the redox reaction.

6 was measured by heating Examples 1 to 3 at 10 ° C./min from room temperature to 900 ° C. in air for accurate experiments with a TGA curve. In the TGA curve of FIG. 6, the weight loss initiation temperature was 637 ° C., and the oxidation temperature was about 650 ° C. at the maximum temperature at the weight loss rate. At about 750 ° C., carbon materials were removed and only Fe material remained.

In FIG. 6, Example 1 (0h) includes Fe at about 26.45 at% in nitrogen-doped graphene, and the Fe is not removed, which is the TGA analysis graph Example 1 (0h) of FIG. 6. 61.7wt%). That is, because the original content of Fe in Example 1 is 67.5wt%.

In Example 2 (3h), Fe was partially removed, and the Fe content was about 33.1 wt%, and in Example 3 (6h), almost all Fe was removed, so that the Fe content was about 5 wt%. In other words, after 6 hours of treatment with HCl, Fe can be seen to be removed.

4) XPS Analysis

In addition, the Fe content in each nitrogen doped graphene for Example 4 to Example 7 with or without the removal of Fe and the heat treatment was carried out at 60 ° C or 90 ° C Table 1 with Example 1, Example 3 4 is shown collectively.

Table 4

sample	XPS Analysis (at.%)
	C	N	Fe	O
Example 1	62.30	4.97	26.45	6.28
Example 3	79.88	7.41	-	12.71
Example 4	63.80	3.54	26.42	6.24
Example 5	83.25	6.13	-	10.62
Example 6	67.63	2.48	26.75	3.14
Example 7	87.82	3.45	-	8.73

From Table 4, by preparing a heat-treated at 1000 ℃ for 45-120 minutes in an N ₂ gas environment in the production of nitrogen-doped graphene, milk powder can be used as a precursor of a nitrogen-doped graphene (N-MLG) synthesis of a multi-layer structure According to the heat treatment time, it was confirmed that the nitrogen content on the nitrogen-doped multilayer graphene (N-MLG) has a distinct effect on the type of nitrogen and the doped nitrogen.

In addition, the prepared nitrogen-doped multilayered graphene (N-MLG) has higher activity than the electrocatalytic activity of the redox reaction of commercially available Pt / C catalysts, undoped graphene, and carbon nanotubes (CNTs). The difference between doped N content and N type was found to be directly related to the ratio of pyridinic-N in particular to the total N atoms.

In addition, the Fe atoms of the nitrogen-doped multilayer graphene do not act as a synergy catalyst for the redox reaction, but it acts as a catalytic growth material for the formation of nitrogen-doped multilayer graphene to promote and stabilize the N atoms. there was.

Therefore, when prepared according to the nitrogen-doped graphene manufacturing method of the present invention, the content of the doped nitrogen can be improved and further control the content of the pyridine-like arrangement, showing excellent electrochemical activity for the redox reaction It seems to be. In addition, Fe can form a graphene-doped multilayer graphene and increase the graphene size while stabilizing the nitrogen atoms functioning and doping as a growth catalyst of graphene, but it is not considered to be functional in the redox reaction.

The above description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present application. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (11)

1. A first step of preparing a mixture solution containing carbon atoms and nitrogen atoms by adding a carbon compound and an amine compound to an acidic solution, followed by heating and stirring to pyrolyze;

   A second step of forming a compound including carbon atoms, nitrogen atoms, and Fe ²⁺ ions by adding and stirring a solution containing Fe ²⁺ ions to the mixture solution containing carbon atoms and nitrogen atoms, and then obtaining them ;

   A third step of forming a Fe substrate by heat-treating the compound obtained in the second step in a nitrogen atmosphere; And

   After the third step, by cooling the carbon atoms and nitrogen atoms contained in the compound comprising a fourth step of forming a nitrogen-doped graphene by diffusing on the Fe substrate, of the nitrogen-doped graphene Manufacturing method.
2. The method of claim 1,

   After passing through the fourth step, further comprising a fifth step of removing the Fe substrate by the reaction by adding an acid, nitrogen-doped graphene manufacturing method.
3. The method of claim 1,

   The nitrogen-doped graphene is a nitrogen-doped multilayer graphene, characterized in that the manufacturing method of nitro doped graphene.
4. The method of claim 1,

   The carbon compound is any one or more selected from the group consisting of proteins, monosaccharides, disaccharides, oligosaccharides, polysaccharides and combinations thereof, nitrogen-doped graphene manufacturing method.
5. The method of claim 4, wherein

   The protein is characterized in that the milk protein, nitrogen-doped graphene manufacturing method.
6. The method of claim 1,

   The solution containing the Fe ²⁺ ions is characterized in that the solution further comprises an ammonium group, nitrogen-doped method for producing graphene.
7. The method of claim 1,

   The amine compound is melamine (C ₃ H ₆ N ₆ ), ammonia (NH ₃ ), hydrazine (NH ₂ NH ₂ ), pyridine (C ₅ H ₅ N), pyrrole (C ₄ H ₅ N), acetonitrile (CH ₃ CN), triethanolamine (C ₆ H ₁₅ NO ₃ ), aniline (C ₆ H ₇ N), 3-aminobenzoic acid (C ₇ H ₇ NO ₂ ), 4-aminobenzoic acid, 3- (4-aminophenyl) Benzoic acid (C ₁₃ H ₁₁ NO ₂ ), 4- (4-aminophenyl) benzoic acid, 4- (3-aminophenyl) benzoic acid (C ₁₃ H ₁₁ NO ₂ ), 5-aminoisophthalic acid (C ₈ H ₇ NO ₄ ), 3- (4-aminophenoxy) benzoic acid (C ₁₃ H ₁₁ NO ₃ ), 4- (4-aminophenoxy) benzoic acid, 3,4-diaminobenzoic acid (C ₇ H ₈ N ₂ O ₂ ), Nitrogen doping, characterized in that the compound of any one selected from the group consisting of 3,5-diaminobenzoic acid, 3-aminobenzoamide (C ₇ H ₈ N ₂ O), 4-aminobenzoamide and combinations thereof Method for producing graphene.
8. The method of claim 1,

   The doped nitrogen is composed of pyridine-like arrangement, pyrrole-like arrangement and graphite-like arrangement, characterized in that the pyridine-like arrangement is 30 to 35%, nitrogen-doped method of producing a graphene.
9. The method of claim 1,

   The heat treatment of the third step is characterized in that carried out in a range of 850 ~ 1200 ℃ under nitrogen atmosphere for 45 ~ 90 minutes, nitrogen-doped graphene manufacturing method.
10. Nitrogen doped graphene produced by the process according to any one of claims 1 to 9.
11. An electrochemical energy device containing nitrogen doped graphene according to claim 11.

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