KR20140127541A - Cu-C nanofiber and methods of fabricating the same - Google Patents

Abstract

The present invention relates to a method for preparing a copper-carbon nanofiber capable of providing oxidation-resistant properties and realizing the simplification of a process, and provides a method for preparing a copper-carbon nanofiber, the method comprising the steps of: forming a copper precursor-organic material nanofiber containing a copper precursor and an organic material; and performing selective oxidative-heat treatment on the copper precursor-organic material nanofiber to oxidize carbon of the organic material and reduce copper of the copper precursor, thereby forming a copper-carbon nanofiber.

Description

[0001] Copper-carbon nanofibers and methods for fabricating the same [0002]

The present invention relates to a nanofiber and a method of manufacturing the same, and more particularly, to a copper-carbon nanofiber and a method of manufacturing the same.

Transparent electrodes are electrode materials that satisfy a certain level of transparency and electrical conductivity and are applied to optoelectronic devices mainly related to light. In order for a transparent electrode to be applied to an actual device, for example, a sheet resistance of 10? /? At 90% transmittance must be satisfied. So far, ITO (indium tin oxide) has been the most widely used and studied material for transparent electrodes. However, such ITO has a problem that the price rise due to the depletion of indium (In) and flexibility are not good. In addition, since deposition is performed through a sputtering process, there is also a process problem that requires a manufacturing environment of a vacuum and a high temperature. In addition, there are problems such as high reflectivity, low inherent conductivity of ITO itself, and reduced conductivity when dissolved.

In this background, research has been conducted to apply CNT (carbon nanotube) and graphene to transparent electrodes. However, in the case of CNT, the electrical conductivity was not good due to the large contact resistance between the nanotubes. In the case of graphene formed by CVD, high electrical conductivity of 30 Ω / □ was observed at a transmittance of 90%. However, when the graphene was produced by a solution process which is easy to mass-produce using a low process ratio and a low temperature process, Have a limit.

In this situation, besides CNTs and graphenes, nanoscale metals have attracted great interest as transparent electrodes. Nanoscale metals that can be applied to transparent electrodes are largely divided into metal thin films, metal nanogrid, metal nanowires, and metal nanofibers.

Referring to FIG. 1, the metal thin film is a film having a thickness of several tens of nanometers, and has a merit that a high level of electrical conductivity of the metal itself can be realized with a certain degree of transmittance through a thin film. In order to increase the transmittance of the metal thin film, the thickness has to be thinned. As the thickness becomes thinner than 15 nm, the resistance increases sharply. This is because as the thickness becomes thinner as in the Fu-S (Fuchs-Sondheimer) and M-S (Mayadas-Shatzkes) models, electrons scatter more on the surface or grain boundary of the metal. As a result, it is necessary to control the thickness of the metal thin film to satisfy a certain level of electrical conductivity and at the same time ensure high transparency. However, since this is not easy, application of transparent electrodes is limited.

Referring to FIG. 2, a metal nanogrid is formed by depositing a grid having a nanometer line width, which is much thicker than a metal thin film for a transparent electrode. As a result, the scattering of electrons is reduced, and a very high electric conductivity (1.6 Ω / □) is obtained at a high transmittance (90%). However, in the case of nano-grid, the process itself requires vacuum and is complicated because it is fabricated by deposition. Therefore, the nanogrid process is much more expensive than other nanoscale metals, and it is difficult to mass-produce.

Referring to FIG. 3, metal nanowires are produced through anisotropic growth of nanoparticles in a solution containing a metal precursor. The thickness of the metal nanowires is from several tens of nanometers to several hundred nanometers, and the length is several tens of micrometers, which is influenced by the concentration of solute such as EDA (ethylene diamine) added in the solution. The most commonly used material for metal nanowires is silver (Ag), which shows a sheet resistance of about 13 Ω / □ at 85% transmittance. Researches on nanowires are currently being conducted, and application studies on the corrosion of silver by H ₂ S and EM (electromigration) phenomenon in actual atmospheric air have been reported. However, silver has the advantages of excellent permeability and conductivity, but it has disadvantages in that it is less advantageous than ITO in terms of price. Finally, in terms of price competitiveness, it is necessary to study metals that are as good as the nanowires but at a low price. And copper (Cu) is the best that can be met. Copper is very low in price compared to silver, but when it is compared with resistivity itself, it is 1.68x10 ^-8 Ω ㆍ m and there is little difference when compared with silver (1.59x10 ^-8 Ω ㆍ m). However, when copper is made into a nanowire structure, it differs in permeability and sheet resistance (60%, 20 Ω / □) because it is much more agglomeration than silver nanowires. The electrical properties of the nanowire are influenced by the resistance of the wire itself and the contact resistance between the wires. The longer and thinner the nanowire is, the better the electrical conductivity. The electrical conduction mechanism of nanowires is based on the percolation theory. More specifically, as nanostructures grow longer, the number of contacts present in series within a certain distance decreases. The thinner the contact, the greater the number of contacts present in parallel within a certain distance, and the effect of inducing a reduction of the total resistance according to the series and parallel distribution of such contacts can be obtained. However, when making nanowires using a solution process, the thickness and length of the wires themselves are determined by the concentration of the solute in the solution. Since the length of the nanowire is also 10 micrometers, the aspect ratio is not so large and the nanostructure itself has a limit in electrical conductivity.

In this background, it is the nanofiber structure (see FIG. 4) that is studied so as to simultaneously obtain the characteristics of silver nano wire while lowering the price by using copper. In other words, metal nanofibers are important because they can provide solutions that overcome the limitations of existing nanowires. Nanofibers can be easily adjusted in thickness and have an aspect ratio of more than 100 micrometers. In addition, it has the advantage of increasing the permeability and conductivity through the arrangement of nanofibers.

Copper nanofiber, which is attracting attention as a promising transparent electrode material, exhibits conductivity and transmittance characteristic comparable to conventional ITO and silver nanowires, but there are still many problems. One of the limitations of these copper nanofibers is the oxidation problem caused by the inherent characteristics of the material copper. Nanofibers are particularly vulnerable to oxidative problems because of their large surface area per volume compared to conventional thin film copper. The problem with copper nanofibers is that they are oxidized and reduced in two steps, which is necessary to make metal nanofibers. The same nanofibers are subject to extreme thermal damage as they are subjected to two successive heat treatments of oxidation and reduction.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for manufacturing copper-carbon nanofibers capable of realizing oxidation resistance characteristics and process simplification. However, these problems are exemplary and do not limit the scope of the present invention.

A process for producing copper-carbon nanofibers according to one aspect of the present invention is provided. The method for producing a copper-carbon nanofiber includes: forming a copper precursor-organic nanofiber including a copper precursor and an organic material; And forming the copper-carbon nanofibers by selectively oxidizing the copper precursor-organic nanofibers so as to oxidize the carbon of the organic materials and simultaneously reduce the copper precursor to copper. Further, the selective oxidation heat treatment is performed in one heat treatment step rather than a plurality of heat treatment steps. One heat treatment step may include a heat treatment step performed under a single condition rather than a multi-step heat treatment step.

In the copper-carbon nanofiber manufacturing method, the selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second partial pressure of oxygen, and in the atmosphere of oxygen partial pressure lower than the first oxygen partial pressure (oxidation point of carbon) When the copper precursor-organic nanofiber is heat-treated, the copper of the copper precursor is reduced and the carbon of the organic material is reduced, and the copper precursor-organic matter When the nanofibers are heat-treated, the copper of the copper precursor may be oxidized and the carbon of the organic material may be oxidized.

When the copper precursor-organic nanofiber is heat-treated in the atmosphere of the first oxygen partial pressure to the second partial pressure of oxygen, the carbon in the copper precursor-organic nanofiber is oxidized and the remaining The residual carbon may support the structure of the copper-carbon nanofibers. When the copper precursor-organic nanofibers are annealed in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, the copper precursor- The residual carbon remaining after the carbon is oxidized can not support the structure of the copper-carbon nanofiber.

Wherein the copper precursor includes copper acetate (Cu (CH ₃ COO) ₂ ), and the organic material is polyvinyl alcohol (PVA) that forms a hydrogen bond with a copper precursor, ). The step of forming the copper-carbon nanofibers by selectively oxidizing the copper precursor-organic nanofibers so as to oxidize the carbon of the organic material and simultaneously reduce the copper precursor to copper may include the steps of: Reducing the copper precursor to copper by using the generated carbon monoxide (CO) as a reducing agent by the selective oxidation heat treatment.

In the method for producing the copper-carbon nanofiber, the copper-carbon nanofiber is formed by coagulating the nanoparticles of the copper uniformly in the direction of the nanofiber in the nanofiber composed of carbon so as to prevent oxidation of the copper Structure, and the nanofiber composed of the carbon may be formed from the organic material.

In the method for producing a copper-carbon nanofiber, the step of forming the copper-carbon nanofiber by selectively oxidizing the copper precursor-organic nanofibers may include a step of thermally decomposing a part of carbon constituting the copper precursor- pyrolysis) into combustion that is not combustion.

In the method for producing a copper-carbon nanofiber, the step of forming the copper precursor-organic nanofiber including the copper precursor and the organic matter may include: providing a solution including the copper precursor, the organic material, and a solvent; And forming the copper precursor-organic nanofibers from the solution by electrospinning using an electrostatic repulsion force formed by applying a high voltage to the solution.

There is provided a copper-carbon nanofiber according to another aspect of the present invention. The copper-carbon nanofiber may be formed by any one of the above-described manufacturing methods. The copper-carbon nanofiber may include copper in the nanofiber composed of amorphous carbon serving as an oxidation preventing layer to prevent oxidation of copper. Nanoparticles are aggregates formed in the direction of nanofibers in a line.

In the copper-carbon nanofiber, copper nanoparticles are dispersed in an amorphous carbon matrix so as to prevent oxidation of copper. The copper nanoparticles aggregate in a longitudinal direction of the nanofiber, core portion of the substrate. Furthermore, the nanoparticles of copper disposed in the core portion of the nanofiber may be arranged to be connected.

According to one embodiment of the present invention as described above, it is possible to provide a method of manufacturing copper-carbon nanofibers that can realize oxidation resistance and process simplification. Of course, the scope of the present invention is not limited by these effects.

1 is a photograph of a metal thin film as a metal nano structure used in a transparent electrode.
2 is a photograph of a metal nano-grid as a metal nanostructure used for a transparent electrode.
3 is a photograph of a metal nanowire as a metal nanostructure used for a transparent electrode.
4 is a photograph of a metal nanofiber as a metal nanostructure used for a transparent electrode.
5 is a flowchart illustrating a method of manufacturing a copper-carbon nanofiber according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating a step of forming copper precursor-organic nanofibers through electrospinning in the method for producing copper-carbon nanofibers according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating a two-step heat treatment of a copper precursor-carbon nanofiber in order to realize copper nanofibers as Comparative Example 1 for comparison with an embodiment of the present invention.
FIG. 8 is a diagram illustrating a concept of a selective oxidation heat treatment process by controlling the partial pressure of oxygen in the one-step heat treatment in the method for producing copper-carbon nanofibers according to an embodiment of the present invention.
9 is a diagram illustrating a process of searching for Gibbs free energy for oxidation reaction of CO serving as a reducing agent in the selective oxidation heat treatment process in the method for producing copper-carbon nanofibers according to an embodiment of the present invention.
FIG. 10 is a diagram illustrating a process of searching for a pressure section capable of performing a selective oxidation heat treatment process in a process for producing copper-carbon nanofibers according to an embodiment of the present invention, using an Ellingham diagram.
11 is a photograph of FE-SEM photographs of nanofiber morphological changes due to solution variables such as viscosity and surface tension of an electrospinning solution in the method of producing copper-carbon nanofibers according to the experimental examples of the present invention.
FIG. 12 is a diagram illustrating a phase change pattern of copper in a selective oxidation heat treatment section in the method of manufacturing copper-carbon nanofibers according to the experimental examples of the present invention.
13 and 14 are TEM diffraction pattern analysis for analyzing the morphology and structure of amorphous carbon in nanofibers formed by selective oxidation heat treatment in the process for producing copper-carbon nanofibers according to the experimental examples of the present invention and FIG. And Raman analysis results.
FIGS. 15 and 16 are diagrams illustrating changes in resistance and nanofiber structure according to pressure in the selective oxidation heat treatment using oxygen gas in the process for producing copper-carbon nanofibers according to the experimental examples of the present invention.
17 is a graph showing the results of evaluating the oxidation resistance of copper-carbon (Cu-C) nanofibers formed by selective oxidation heat treatment in the method for producing copper-carbon nanofibers according to the experimental examples of the present invention.
18 is a graph showing conductivity and transmittance characteristics of the oxidation-resistant copper-carbon (Cu-C) nanofiber fabricated by the selective oxidation heat treatment in the method for producing copper-carbon nanofibers according to the experimental examples of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, for convenience of explanation, the components may be exaggerated or reduced in size.

5 is a flowchart illustrating a method of manufacturing a copper-carbon nanofiber according to an embodiment of the present invention.

Referring to FIG. 5, a method of fabricating a copper-carbon nanofiber according to an exemplary embodiment of the present invention includes providing a solution including a copper precursor, an organic material, and a solvent (S10) (S20) of forming the copper precursor-organic nanofibers from the solution by electrospinning using electrostatic repulsion; and oxidizing the carbon of the organic substance and simultaneously oxidizing the copper precursor to copper (S30) by selectively oxidizing the copper precursor-organic nanofibers to reduce the copper-carbon nanofibers. In particular, the selective oxidation heat treatment is performed in one heat treatment step rather than a plurality of heat treatment steps. The one heat treatment step may include a heat treatment step performed under a single condition rather than a multi-step heat treatment step.

FIG. 6 is a diagram illustrating a step of forming copper precursor-organic nanofibers through electrospinning in the method for producing copper-carbon nanofibers according to an embodiment of the present invention.

Referring to FIG. 6, a solution 22 made by mixing a metal precursor, organic matter, and a solvent in a syringe 10 for electrospinning is placed. Electrospinning is a simple and highly efficient method of making the nanofibers 24 by applying a high voltage to the solution 22 and using electrostatic repulsion. The solution 22 used to produce the nanofibers 24 may comprise a metal solid solution such as a metal precursor, an organic matrix (organic), and a solvent. The metal solid solution is a material containing the ions of the metal nanofiber 24 to be formed, and the combination between the functional groups in the solid solution and the organic matrix is important. Thus, it may be desirable to select materials having the same or similar types of functional groups and to make the dispersion of the metal solid solution uniform. For example, the metal precursor may comprise copper acetate (Cu (CH ₃ COO) ₂ ) to make copper nanofibers. The organic material, that is, the organic matrix, acts as a skeleton of the nanofiber 24 that is first formed through electrospinning. For example, to make copper nanofibers, the organic matrix forms a hydrogen bond with an acetate group (-CH ₃ COO-) of copper acetate (CuAc) and a polyvinyl alcohol (PVA) with a relatively low decomposition temperature . The solvent should be able to dissolve both the metal solid solution and the organic matrix. For example, to make copper nanofibers, the solvent may use distilled water because the solubility of copper acetate and polyvinyl alcohol in water is relatively high.

For example, the copper precursor-carbon nanofibers 24 are fabricated through electrospinning, which produces fibers by applying electrostatic repulsion to the solution 22. The copper precursor-carbon nanofiber 24 formed by electrospinning is subjected to oxidation and reduction followed by calcination to obtain a copper nanofiber. In the electrospinning, the thickness of the nanofibers generated according to the magnitude of the voltage of several tens kV applied to the solution 22 can be easily controlled, and the length can also be more than 100 μm. Further, the nanofiber array has an advantage that the transmittance and the conductivity can be further improved. These metal nanofibers are important because they can provide a solution that can overcome the limitations of existing nanowires.

The process of forming the nanofibers 24 is greatly influenced by the parameters of the solution 22. The shape of the nanofibers 24 produced by electrospinning depends on the viscosity of the solution 22, the surface tension, the concentration of the organic matter, the molecular weight, and the conductivity of the solvent. Among them, the viscosity of the solution (22) may have the greatest influence on the solution variables. If the viscosity is very low or very high, a bead is formed in the nanofiber 24, which is not suitable for the transparent electrode. Therefore, in order to obtain the shape of the nanofiber suitable for the transparent electrode, it is necessary to optimize the conditions by adjusting the viscosity of the solution and other solution parameters.

In the process of forming the nanofibers 24, besides the solution variables, there are electrospinning process variables and environmental variables. Environmental variables include humidity and temperature, because the optimal conditions for electrospinning are fixed, so that the atmosphere can be controlled by creating an environment that can meet them. The variables affecting the nanofibers (24) more directly than the environmental variables are electrospinning process variables. The electrospinning process parameters include the magnitude of the voltage applied by the high voltage source 12, the distance between the tip 11 and the collector 14, and the feeding rate of the solution 22. Of these, the applied voltage is related to the electrostatic repulsive force which directly affects the formation of the nanofibers 24 in the solution 22. The larger the applied voltage is, the smaller the diameter of the nanofiber 24 is, but if it is too large, it causes instability in the electrospinning itself. Therefore, it is possible to form optimized nanofibers that can be applied to transparent electrodes by establishing the condition of these solution variables and process variables.

Next, a process for selectively oxidizing the copper precursor-carbon nanofibers 24 in order to realize oxidation-resistant copper-carbon nanofibers by a one-step heat treatment will be described. First, before describing the selective oxidation heat treatment method according to the technical idea of the present invention, a two-step heat treatment method in which an oxidation heat treatment and a reduction heat treatment are sequentially performed is referred to as Comparative Example 1, and a self-reduction heat treatment The method will be described below as Comparative Example 2.

FIG. 7 is a diagram illustrating a two-step heat treatment of a copper precursor-carbon nanofiber in order to realize copper nanofibers as Comparative Example 1 for comparison with an embodiment of the present invention. Referring to FIG. 7, the copper precursor-carbon nanofiber 24 is a composite nanofiber comprising copper acetate as the metal precursor 24a and polyvinyl alcohol as the organic material 24b. Subsequent heat treatment is required to make the copper precursor-carbon nanofibers 24 into the copper nanofibers 26. Heat treatment is performed in the air to oxidize and decompose the organic precursor 24b present in the copper precursor-carbon nanofiber 24. As a result, the copper in the metal precursor 24a is oxidized to copper oxide (CuO), and the carbon of the organic material 24b is oxidized to be completely decomposed. Thus, copper oxide (CuO) nanofiber 25 is finally formed. This copper oxide nanofiber 25 should be reduced again to make pure copper nanofiber 26. Therefore, heat treatment may be performed in a hydrogen (H ₂ ) gas atmosphere for reduction to produce the final copper nanofiber 26. That is, in order to produce the metal nanofibers 26, a two-step heat treatment process of oxidation and reduction is required. The reasons for the oxidation and reduction are as follows. First, the oxidation is to remove the organic material 24b in the form of an organic matrix used to make the nanofiber structure in electrospinning. In this process, hydrogen gas is used to reduce the copper oxide formed by oxidizing the copper together. The same nanofibers are subjected to two successive heat treatments opposite to each other for oxidation and reduction, resulting in severe damage. Further, the manufacturing process is complicated and manufacturing costs are increased.

As a method for solving this, as a comparative example 2 for comparison with an embodiment of the present invention, a self-reduction heat treatment method for reducing both carbon and oxygen will be described. Comparative Example 2 is characterized in that in the first heat treatment in Comparative Example 1, the oxygen partial pressure is extremely lowered to induce auto-reduction in an atmosphere where oxidation does not occur. Self-reduction refers to a heat treatment method in which a precursor with an acetate functional group, such as copper acetate, is used to directly reduce to copper. Such self-reducible metals satisfy the conditions that the oxidation reactivity is lower than that of carbon such as nickel, cobalt, and iron, including copper. In the present invention, a basic experiment in which a copper precursor (CuAc) was autolored and applied to the production of nanofibers was conducted. When argon gas is used to heat the oxygen partial pressure lower than the copper and the carbon can be oxidized, the carbon undergoes a pyrolysis reaction, and the copper becomes copper directly without being oxidized by the self-reduction. The nanofibers produced by this method exhibit a constant ohmic contact behavior as in a conventional conductor. However, the copper nanofibers produced by the autothermal reduction compared to the copper nanofibers produced through the two-step heat treatment in Comparative Example 1 were not completely decomposed because the carbon was not oxidized. As a result of the residual carbon, It has a disadvantage that conductivity is low.

The selective oxidation heat treatment process according to one embodiment of the present application is introduced to solve these problems. That is, in one embodiment of the present invention, a method of making a nanofiber having a high oxidation stability by a single step of a heat treatment process by controlling the oxygen partial pressure in the heat treatment after the electrospinning is proposed. This is possible by fully understanding and applying the oxidation reactivity and change of copper and carbon with oxygen partial pressure. In the conventional two-stage heat treatment (Comparative Example 1), copper and carbon are both oxidized under the condition of heat treatment for oxidation. As a result, all of the carbon is oxidized, but the copper is oxidized, which requires additional heat treatment for reduction. The ordinary copper nanofibers produced through such a process are directly exposed to the outside of the crystalline copper, and the oxidation proceeds very rapidly because the surface area per volume is large.

Conversely, pure copper can be obtained immediately after the first stage heat treatment (Comparative Example 2) in an atmosphere in which copper and carbon are both reduced by lowering the oxygen partial pressure to induce self-reduction. However, since carbon is not oxidized and completely decomposed into combustion, but decomposed by pyrolysis, residual carbon remains to a certain extent. The nanofibers produced by this method are formed in such a structure that the copper nanoparticles are densely dispersed in the amorphous carbon. It is known that the electrical conduction of the copper nanoparticles arranged in the amorphous carbon matrix is achieved by electron hopping. When the actual resistance is measured, it is confirmed that the ohmic contact is formed. However, the copper-carbon nanofiber formed through the self-reduction has a disadvantage that the electrical resistance is relatively high because the amount of the residual carbon is large and the conductivity is not good.

The two types of subsequent heat treatment methods introduced in the above comparative examples are different from the heat treatment methods proposed in the embodiment of the present invention in that copper and carbon are both oxidized or reduced. In an embodiment of the present invention, a selective oxidation method is proposed in which copper is reduced and carbon is oxidized and decomposed using the difference in oxidation reactivity between carbon and copper. This is significant because it has both advantages of heat treatment in air atmosphere and advantages of heat treatment through self reduction. That is, the copper is directly reduced through the first-stage heat treatment by self-reduction, and the amount of residual carbon is reduced because the carbon can be decomposed through oxidation. That is, the copper is cohered in a line along the axis parallel to the nanofiber, and the surface of the copper is surrounded by the amorphous carbon serving as the oxidation preventing film. In these comparative examples, it is possible to produce nanofibers having an electrical conductivity higher than that of the self-reduction, together with an antioxidant function not possessed by the copper nanofibers.

8 is a view illustrating the concept of the selective oxidation heat treatment process in the method for producing copper-carbon nanofibers according to an embodiment of the present invention.

Referring to FIG. 8, after forming a copper precursor-organic nanofiber including a copper precursor and an organic material, the copper precursor-organic nanofiber is oxidized to oxidize the carbon of the organic material and simultaneously reduce the copper precursor to copper. The organic nanofibers are selectively oxidized by a single heat treatment step rather than a plurality of heat treatment steps to form the copper-carbon nanofibers. In this case, the selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure (i.e., a first oxygen partial pressure or more and a second oxygen partial pressure or less), wherein in the atmosphere of the oxygen partial pressure lower than the first oxygen partial pressure, In the case where the copper precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, when the organic precursor-organic nanofibers are heat-treated, the copper of the copper precursor is reduced and the carbon of the organic substances is reduced. The copper of the organic material is oxidized and the carbon of the organic material is also oxidized. For example, the first oxygen partial pressure may be an oxygen partial pressure corresponding to an oxidation point of carbon, and the second oxygen partial pressure may be an oxygen partial pressure corresponding to an oxidation point of copper.

When the copper precursor-organic nanofibers are heat-treated in the atmosphere of the first oxygen partial pressure to the second partial pressure of oxygen, residual carbon remaining in the copper precursor-organic nanofiber is oxidized by the copper- If the copper precursor-organic nanofiber is subjected to heat treatment in an atmosphere having an oxygen partial pressure higher than the second partial pressure of oxygen, since the carbon in the copper precursor-organic nanofiber is oxidized, Even if the structure of the fiber is collapsed or the nanofiber is formed, the copper comes into direct contact with the outside and the oxidation resistance becomes weak.

According to one embodiment of the present invention, there is proposed a selective oxidation method in which copper is reduced and only carbon is oxidized and decomposed using the difference in oxidation reactivity between carbon and copper. In a conventional air atmosphere, It has a great significance because it has both the advantages of heat treatment and the advantages of heat treatment through self-reduction. The copper-carbon nanofiber realized by the selective oxidation heat treatment includes a structure in which nanoparticles of copper are aggregated in the longitudinal direction of the nanofibers in a line in the nanofiber composed of amorphous carbon so as to prevent oxidation of copper. Furthermore, the copper nanoparticles disposed on the copper-carbon nanofibers have a relatively higher density inside the nanofiber corresponding to the core portion of the nanofiber, and a relatively low density As shown in Fig. Further, the copper nanoparticles agglomerating in a line in the core (core) are arranged to be connected to each other, thereby securing the electrical conductivity characteristics of the nanofibers.

On the other hand, in the copper-carbon nanofiber realized by the autothermal reduction treatment, the copper nanoparticles are uniformly distributed throughout the fiber without having a high dispersion density in the core of the fiber (see the self-reduction heat treatment The nanoparticles of the copper are uniformly dispersed throughout the fiber, considering that the fibers are overlapped with each other. Further, in the copper-carbon nanofiber realized by the autothermal reduction treatment, the copper nanoparticles are relatively unevenly distributed and are arranged in a relatively large size, so that the copper nanoparticles are aggregated in a line so as to be connected to each other in the fiber The electrical conductivity is relatively lower than that of the nanofiber realized by the selective oxidation heat treatment. Therefore, the copper-carbon nanofibers realized by the selective oxidation heat treatment can have improved electrical conductivity than the self-reduction with the antioxidant function that copper nanofibers have in these comparative examples.

The copper reduction process in the selective oxidation heat treatment process according to an embodiment of the present invention can be applied to at least a part of the self reduction method described above. For example, nanofibers made from a solution containing copper acetate as a metal precursor, polyvinyl alcohol (PVA) as a polymer matrix, and water as a solvent are mixed in a high vacuum (10 ^-5 to 10 ^-6 Torr) or argon gas atmosphere, a reaction as shown in Chemical Formulas 1 to 4 occurs in the metal precursor.

(Formula 1)

Cu (CH ₃ COO) _{2 -} > CuCO ₃ + CH ₃ COCH ₃

(2)

CuCO _{3 -} > CuO + CO ₂

(Formula 3)

CH ₃ COCH _{3 -} > CO + C ₂ H ₆

(Formula 4)

CuO + CO → Cu + CO ₂

By this reaction, a reducing agent (for example, carbon monoxide (CO)) is automatically generated in the acetate, and a pure copper phase can be obtained during the heat treatment process.

Hereinafter, it will be described from the thermodynamic point of view that a selective oxidation heat treatment process can be performed in the process for producing copper-carbon nanofibers according to an embodiment of the present invention.

9 is a diagram illustrating a process of searching for Gibbs free energy for oxidation reaction of CO serving as a reducing agent in the selective oxidation heat treatment process in the method for producing copper-carbon nanofibers according to an embodiment of the present invention. The reduction of copper acetate (CuAc), which is a metal precursor used in the selective oxidation heat treatment, is due to carbon monoxide (CO), which is a reducing agent generated during the heat treatment in the acetate functional group. That is, copper is reduced by self-reduction even in the selective oxidation heat treatment process. Therefore, in order to find the oxygen partial pressure required in this heat treatment, the reaction of copper generated in the autothermal reduction should be considered.

  First, when copper acetate is decomposed, copper oxide is reduced by carbon monoxide (CO) after copper oxide (CuO) is formed. Therefore, the Gibbs free energy for the oxidation reaction of carbon monoxide must be confirmed in the Elling diagram. In the actual E-ring diagram, the oxidation reaction of carbon monoxide is not shown, so it is necessary to utilize the reaction in which carbon is oxidized to form carbon monoxide and carbon dioxide. When the reaction in which carbon monoxide is formed (the green line in Fig. 9) is reversed in the reaction in which carbon dioxide is formed (the red line in Fig. 9), the actual carbon monoxide is oxidized at a given temperature and pressure to become carbon dioxide The yellow line). It should be noted that as the autoregression proceeds, the graph of the oxidation reactivity of carbon monoxide increases. This is due to the ratio of carbon monoxide and carbon dioxide in the Elling diagram, which is the result of carbon monoxide being consumed by autothermal reduction, resulting in carbon dioxide.

10 is a diagram illustrating a process of searching for a pressure section capable of performing a selective oxidation heat treatment process in the process for producing copper-carbon nanofibers according to an embodiment of the present invention, In order to find the oxygen partial pressure for the selective oxidation heat treatment, the Gibbs free energy for the oxidation reaction of the carbon monoxide obtained through a series of processes should be indicated in the Ellingham diagram and then compared with the actual oxidation reaction of copper. Unlike bulk systems, nanostructures such as nanofibers increase the surface energy because of the large surface area per volume. This has the effect of increasing the total Gibbs free energy by Equation (1).

Because of this, the Gibbs free energy is larger than the bulk by a certain amount, so that the oxidation reaction energy can be translated in the y-axis direction. The pressure at which the phase change tendency of the copper was confirmed in the basic experiment and the oxygen partial pressure at that time can be expressed as shown in FIG. Basic Experiments In the first result, Cu ₂ O and Cu phases were obtained when heat treatment was performed at 500 ° C (green line in FIG. 10) at an oxygen partial pressure of PO ₂ = 10 ^-6 atm. If the oxygen partial pressure is further lowered under this condition, a pure Cu phase can be obtained. The temperature and oxygen partial pressure at this time are 500 ° C. and P _O2 = 10 ^-9 atm. The basic experiment shows that these conditions are in the selective oxidation heat treatment section to be studied in this study. Then, it is possible to carry out the experiment in the direction of confirming the phase change and the decomposition of copper and carbon by proceeding the heat treatment under the condition of the oxygen partial pressure, and finally, the best conductivity characteristic and the antioxidant effect The condition can be found.

 Hereinafter, experimental examples are provided to facilitate understanding of the present invention. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and are not intended to limit the scope of the present invention.

First, an experimental method of various conditions will be described.

Establish optimized solution and process parameter conditions

It is aimed to establish the optimal conditions by analyzing the tendency depending on the solution and the process parameters affecting the morphology of nanofibers. Copper acetate (Cu (CH ₃ COO) ₂ ) is used as a metal precursor to make copper nano fiber, which is one of the materials which is seen as a transparent electrode material because it shows high price competitiveness and electric conductivity. The organic matrix is intended to constitute the skeleton of nanofibers using poly vinyl alcohol (PVA), which forms a hydrogen bond with an acetate group (-CH ₃ COO-) and has a relatively low decomposition temperature. Both of these materials have the advantage of being able to make solutions using distilled water because of their relatively high solubility in water.

<Solution variable>

We try to establish the solution condition by changing the viscosity of the solution which directly affects the morphology of nanofibers. The molecular weight and concentration of the organic matrix PVA are controlled to control the viscosity. The shape of nanofibers according to the change of viscosity is analyzed by FE-SEM and the conditions of viscosity in which the nanofibers are formed in the optimal form are presented.

<Process Variables>

The change of the nanofiber shape according to the applied voltage to the solution in the syringe containing the electrospinning solution, the distance between the syringe tip and the collector, and the solution injection speed was analyzed by FE-SEM, The process parameter condition is established.

Subsequent heat treatment process: oxygen partial pressure setting for selective oxidation heat treatment

In order to proceed with the selective oxidation heat treatment, it is important to adjust the oxygen concentration in the chamber in which the subsequent heat treatment is performed. Experiments were carried out by setting the pressure on the basis of inference in the E-ring diagram. The metal precursor formed by electrospinning + organic matrix nanofibers was subjected to a subsequent heat treatment by controlling the pressure in a CVD or electric furnace using a vacuum pump Respectively.

Phase change and decomposition of copper and carbon in selective oxidation heat treatment

After the heat treatment, the phase change of copper in nanofiber was analyzed by XRD. In the case of metal precursors and organic matrix nanofibers made in solution by electrospinning, crystal peaks are not seen in XRD because they show no crystallinity. However, XRD is suitable for distinguishing the types of nanofibers obtained through heat treatment because the crystal nuclei or copper nanofibers obtained through the subsequent heat treatment show definite crystallinity and the crystal peak positions appearing in XRD are different depending on each kind. FE-SEM and TEM were used for the morphology and microstructure analysis of nanofibers.

Analysis of decomposition phenomenon by carbon structure and oxidation

In the selective oxidation heat treatment, it is premised that carbon is decomposed by combustion. Therefore, an experiment should be conducted to confirm that the carbon has been decomposed. First of all, it is necessary to analyze the structure of carbon in the nanofibers when the heat treatment is performed in an atmosphere in which the degree of vacuum is reduced to 10 ^-6 Torr or the oxygen partial pressure is made very low using argon gas. TEM images, diffraction pattern analysis and Raman analysis were performed to determine the crystallinity and phase of carbon. After verifying the presence of such carbon in the nanofibers, the amount of copper and carbon was measured using FE-SEM EDS to analyze the degree of carbon decomposition in the actual selective oxidation heat treatment. Through this analytical method, the decomposition of carbon in the selective oxidation heat treatment can be confirmed.

Amorphous On the carbon film  by Cu -C Evaluation of Antioxidant Properties of Nanofibers

The structure of the nanofiber fabricated by the selective oxidation heat treatment is in the form of copper nanoparticles dispersed in the amorphous carbon matrix. From the standpoint of copper nanoparticles, it can be said that the outer surface is covered with a carbon film having higher oxidation reactivity than copper. Based on this structure, experiments were conducted to evaluate the antioxidant performance of nanofibers. The test was carried out by measuring the sheet resistance for 28 days at room temperature and air, and observing the degree of change. The control was set to copper nanofibers prepared by the heat treatment in the two-step process described in Comparative Example 1 and compared with copper-carbon (Cu-C) nanofibers produced by selective oxidation heat treatment.

Measurement of permeability and sheet resistance of nanofiber with antioxidant properties

Since it is a metal nanofiber for application to a transparent electrode, it is very important to evaluate the transmittance and electrical conductivity characteristics thereof. The transmittance was measured by UV-Vis spectroscopy, which measures the absorbance of the sample using light from ultraviolet to visible light. This can be used to evaluate the optical properties of nanofibers made by electrospinning and subsequent heat treatment processes. Conductivity characteristics of nanofibers are analyzed by surface resistance measured by 4 point contact using van der pauw method. The substrate was a silicon oxide (SiO ₂ ) wafer or a quartz glass. Through the measured permeability and sheet resistance, we compared the physical properties required for the conventional copper nanofiber fabricating process and the transparent electrode of the copper - carbon nanofiber fabricated by the new process.

Hereinafter, experimental results derived by the above-described experimental methods of various conditions will be described.

Formation of optimal nanofiber structure by solution variable control

FIG. 11 is a photograph of the morphological change of nanofibers due to solution parameters such as viscosity and surface tension in the process for producing copper-carbon nanofibers according to the experimental examples of the present invention. Referring to FIG. 11, the structure of nanofibers formed through electrospinning is greatly influenced by the viscosity, surface tension, conductivity, etc. of the electrospinning solution. Among them, the viscosity of the solution has the greatest influence on the formation of beads in the nanofiber itself, so that it is necessary to control the viscosity of the solution first. The viscosity is affected by the molecular weight or concentration of the polymer matrix in the solution. In this example, the concentration was controlled. Based on this point of view, the best nanofiber morphology was obtained at the concentration of 15 wt%. In addition to this, a process of controlling the surface tension of the solution itself is also required. It is also necessary to control the morphology of the nanofibers and to prevent aggregation at the end of the syringe needle (11 in FIG. 6) when electrospinning with the actual solution. The surface tension of the electrospinning solution can be reduced by mixing ethanol having a smaller surface tension than that of water. Optimum conditions can be found in this experiment depending on the mixing ratio of water and ethanol. After optimizing the solution production rate, the electrospinning was carried out, and then a subsequent heat treatment process, which was emphasized in this experiment, was carried out.

Phase Change Behavior of Copper in Selective Oxidation Heat Treatment

FIG. 12 is a diagram illustrating a phase change pattern of copper in a selective oxidation heat treatment section in the method of manufacturing copper-carbon nanofibers according to the experimental examples of the present invention. Nanofibers of copper acetate (CuAc) and organic matrix (PVA) were prepared by electrospinning, and then selective oxidation treatment was performed while controlling the degree of vacuum in the subsequent heat treatment process. In the selective oxidation heat treatment, since copper is a reduced oxygen partial pressure, copper should be reduced so that copper oxide is not formed. In order to confirm this, the copper phase was analyzed by XRD analysis after executing the pressure within the set pressure based on the Elling diagram before the heat treatment. The Cu ₂ O phase was formed at a pressure capable of selective oxidation heat treatment (3.8 × 10 ^-3 Torr). However, when the pressure was gradually decreased to increase the degree of vacuum up to 8 × 10 ^-4 Torr, copper oxide was not formed but gradually pure copper phase was formed. In other words, when the selective oxidation heat treatment was carried out, the XRD analysis revealed that the copper was reduced without being oxidized in the intended direction.

The combustion of carbon in the selective oxidation heat treatment (combustion)

FIGS. 13 and 14 illustrate TEM diffraction pattern analysis for the morphology and structure analysis of amorphous carbon in nanofibers formed by pyrolysis in the process for producing copper-carbon nanofibers according to the experimental examples of the present invention, These are the drawings showing the results of the raman analysis.

One of the most important aspects of selective oxidation heat treatment is the decomposition of carbon in the nanofiber by oxidizing it. As in Comparative Example 2 described above, the amount of residual carbon was very large in the case of the self-reducing copper that was directly formed by the subsequent heat treatment in the first step, because carbon decomposed into pyrolysis rather than combustion. However, if carbon can be decomposed by burning, which is a type of oxidation reaction, the amount of residual carbon can be greatly reduced, which can lead to automatic improvement of electrical conductivity.

A TEM diffraction pattern was analyzed to examine the crystal phase and structure of carbon present in the nanofibers (see FIG. 13). As a result, an amorphous carbon pattern was confirmed, not a pattern of a substance having crystallinity. Also, the results of the Raman analysis (see FIG. 14) reveal that there is a 2D peak for a crystalline carbon such as CNT, graphene, and graphite, but no 2D peak is found for the carbon obtained from this experimental example. From these analyzes, it can be seen that the carbon before decomposition by the selective oxidation heat treatment is amorphous. The amorphous carbon is to be decomposed in the selective oxidation heat treatment.

Conductivity and structural change of nanofiber with oxygen pressure

FIGS. 15 and 16 are diagrams illustrating changes in resistance and nanofiber structure according to pressure in the selective oxidation heat treatment using oxygen gas in the process for producing copper-carbon nanofibers according to the experimental examples of the present invention.

This experiment was conducted to investigate the pressure with the highest electrical conductivity through the selective oxidation heat treatment. In order to improve the electrical conductivity, the pressure in the oxygen gas heat treatment was set in the range of 10 ^-2 Torr to 10 ^-1 Torr to confirm the sheet resistance according to each condition. The FE-SEM analysis was also performed to confirm the structure of the nanofibers formed under each condition.

The change of sheet resistance showed different behavior based on 2.5 × 10 ^-2 Torr. Were thus resistance is reduced as 10 ^-2 Torr, the pressure increased up to 2.5x10 ^-2 Torr in, which can be thought of these causes in that it is decomposed by combustion of the residual carbon more smoothly with increasing pressure. It can also be seen from FIG. 13 that the copper is agglomerated in the nanofibers in a line and the surface is composed of amorphous carbon in a well-formed nanofiber structure at 2.5 × 10 ^-2 Torr in the FE-SEM image 13). On the contrary, when the oxygen partial pressure is further increased at 2.5 × 10 ^-2 Torr and the decomposition of the residual carbon is further increased, the resistance increases as the pressure increases. This is because the residual carbon is decomposed more and more beyond the limit of maintaining the nanofiber structure, so the nanofiber structure is gradually collapsed and the resistance is expected to increase. The IV curves showed that the oxygen partial pressures continued to increase, but the behavior was not observed until 6 × 10 ^-2 Torr.

Anti-oxidation effect of copper nanofiber by amorphous carbon film

17 is a graph showing the results of evaluating the oxidation resistance of copper-carbon (Cu-C) nanofibers formed by selective oxidation heat treatment in the method for producing copper-carbon nanofibers according to the experimental examples of the present invention.

In the selective oxidation heat treatment using oxygen gas, it was confirmed that 2.5 x 10 ^-2 Torr is the optimum electrical conductivity. The nanofibers made by this method are composed of a nanofiber matrix of amorphous carbon which acts as an oxide film, and copper nanoparticles are aggregated in a line in the direction of the nanofibers. Therefore, unlike pure copper nanofiber, it has the structural advantage of being able to be protected from direct contact with the external environment. Based on this structure, the anti-oxidation characteristics of the copper-carbon (Cu-C) nanofiber developed in this study were measured. The conditions were the same as the normal environment of the device, and the temperature was measured at room temperature and air for 28 days. As a control, copper nanofibers were used.

As a result of examining the resistance change caused by the oxidation of copper in the two nanofibers, it was found that the resistance increases only to about 10% for 28 days in the copper-carbon (Cu-C) nanofiber unlike the copper nanofiber set as the control I could confirm. In the case of the copper nanofiber set as the control group, the resistance increased at a very rapid rate, which is 12 times higher than that of the conventional copper nanofiber.

In order to prevent oxidation of copper nanofibers as well as the control group, we compared the results with reference to the research data on the prevention of oxidation by covering the coating film with ALD method. In this experiment, oxidation was also carried out at room temperature, atmospheric pressure, and air atmosphere, where the pure copper nanofibers increased by 60% after 28 days. Therefore, when these control groups are checked, it can be concluded that the copper-carbon (Cu-C) nanofiber according to the present invention has a certain antioxidant ability.

In the case of Cu-C nanofibers, it has great significance in that an antioxidant film is formed from PVA added to the solution to make the nanofiber structure. In the case of covering the outer layer with ALD as in other studies for oxidation resistance, the process is further added and inefficient in terms of material. However, the method proposed in the present embodiments is not limited to the carbon fiber of the nanofiber formed by electrospinning But it is significant in that it is controlled by selective oxidation heat treatment in an effective structure and thickness to prevent oxidation.

Conductivity and permeability of nanofibers formed by selective oxidation heat treatment

18 is a graph showing conductivity and transmittance characteristics of the oxidation-resistant copper-carbon (Cu-C) nanofiber fabricated by the selective oxidation heat treatment in the method for producing copper-carbon nanofibers according to the experimental examples of the present invention.

The permeability and electrical conductivity (sheet resistance) of copper-carbon (Cu-C) nanofiber with anti-oxidation properties were measured. The permeability and sheet resistance of copper-carbon (Cu-C) nanofibers were lower than those of pure copper nanofibers. Determining permeability and sheet resistance is related to the inherent electrical conductivity of the nanofiber itself. Again, if the conductivity of the nanofiber itself is high, the conductivity of the nanofiber membrane is assured even with a smaller number of nanofibers. In the nanofiber structure, light is transmitted through an area where there is no nanofiber. That is, it can be seen that the smaller the number in the unit area, the better the permeability. From this point of view, it is necessary to improve the conductivity of the nanofiber itself in order to increase the permeability and conductivity of the copper-carbon (Cu-C) nanofiber. Therefore, nanofibers can be made using other polymers with crystallinity instead of PVA, or by controlling the ratio of copper acetate to organic material (PVA) by approaching the process of making the solution again, not by subsequent heat treatment.

Hereinafter, experimental methods and results of the various conditions described above will be summarized.

Present a new heat treatment process based on thermodynamic theory

In this experimental example, the purpose of the present invention was to solve the problems in the process and reliability of the copper nanofiber, which is a transparent electrode. Electrospinning is a process for preparing nanofibers by applying a solution made by mixing a metal precursor (CuAc), a polymer matrix (PVA) and a solvent (water) into a syringe and applying a high voltage. In order to make CuAc + PVA nanofiber thus formed into copper nanofiber, it is necessary to heat treatment in air atmosphere for oxidation and heat treatment in hydrogen atmosphere for copper reduction. The process of making this method has the purpose of decomposing carbon by oxidation and obtaining pure copper. This causes extreme damage to the nanofibers in that it causes the opposite reactions to occur sequentially because of repeated oxidation and reduction processes. In addition, since hydrogen gas is used and it is inefficient, a solution was needed.

In order to solve these process problems, we have approached the heat treatment process of nanofibers from a thermodynamic point of view. Conventionally, if both copper and carbon are oxidized at a high oxygen partial pressure, the present invention proposes a heat treatment using difference in oxidation reactivity between copper and carbon. In this experimental example, since carbon is oxidized more easily than copper, heat treatment is performed under the condition that only carbon is oxidized and copper can be reduced. In other words, this is a strategic heat treatment method that selectively oxidizes carbon, which is defined as selective oxidation heat treatment.

Through the selective oxidation heat treatment, the phase change of copper and the decomposition by combustion of carbon were proved through basic experiments. Within the pressure range expected to allow selective oxidation heat treatment through the Ellingham diagram, the copper reduction was confirmed by XRD. And we have found through the TEM diffraction pattern, Raman analysis, that carbon exists in amorphous form in nanofiber. It was also found that when the carbon was selectively oxidized, it could be completely decomposed.

The selective oxidation heat treatment proposed in this experiment is of great significance for the first time that the method of heat treatment of nanofibers is approached from the thermodynamic point of view. From the thermodynamic point of view, there will be a lot of applications in the future because it does not make pure copper nanofibers through two steps and oxidizes only carbon through pressure control without using hydrogen gas as a first step heat treatment method It is expected. In other words, it can be said that it is possible not only to use these nanofiber heat treatments but also to apply heat treatment by applying these theories to various other fields.

Development of oxidation-resistant Cu-C nanofibers formed through one-step heat treatment

Among the results obtained in this experimental example, the most significant achievement is the development of oxidation-resistant copper-carbon (Cu-C) nanofiber. It is also very meaningful that the oxidation-resistance is achieved only by the one-step heat treatment method in that it can be produced by the above-mentioned selective oxidation heat treatment method. Regarding the structure of the copper-carbon (Cu-C) nanofiber, the nanofiber is a matrix of amorphous carbon and forms the skeleton of the nanofiber. And copper nanoparticles are densely arranged inside the carbon matrix. In other words, copper nanoparticles can be seen as a structure in which all the particles are covered by one particle, and these particles are continuously connected in the form of nanofibers. Taking a look at the advantages of this structure, as described above, oxidation occurs first because carbon is more oxidative than copper. This means that when nanofibers are present in conditions that can be oxidized, carbon is oxidized instead of copper. Another advantage is the electrical conduction mechanism of the nanofibers. Common copper nanofibers are crystalline copper in which the medium through which electrons are transferred is continuous. Therefore, the oxidation of copper can have a significant effect on the transfer of electrons. However, in the copper-carbon (Cu-C) nanofiber proposed in this experimental example, electrons follow a mechanism of hopping between the copper nanoparticles. Therefore, this is greatly influenced by the distance between the copper nanoparticles, and the electron migration is not greatly influenced by the degree of oxidation of carbon in the middle. This conduction mechanism is also an optimal form for oxidation resistance.

The oxidation-resistant copper-carbon (Cu-C) nanofiber formed through the first-stage heat treatment process is of great importance in that it solves the very large problem of oxidation that copper has previously brought about. And this method is a great advantage that the oxidation resistance function is given by reusing the material that was necessary to make the nanofiber, unlike the conventional method in which the coating process is added by coating the outer surface in order to solve the oxidation problem. This technology is very likely to be applied not only to transparent electrodes but also to various fields where copper can be used as an electrode now.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: Syringe
22: solution
24: Copper precursor-carbon nanofibers
24a: metal precursor
24b: organic matter
25: Copper oxide (CuO) nanofiber
26: Copper nanofiber

Claims (10)

Forming a copper precursor-organic nanofiber comprising a copper precursor and an organic material; And
Forming copper-carbon nanofibers by selectively oxidizing the copper precursor-organic nanofibers to oxidize carbon of the organic material and simultaneously reduce the copper precursor to copper,
Wherein the selective oxidation heat treatment is performed in one heat treatment step rather than a plurality of heat treatment steps. The method according to claim 1,
The selective oxidation heat treatment is performed in an atmosphere of a first oxygen partial pressure to a second oxygen partial pressure,
When the copper precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure lower than the first oxygen partial pressure, copper of the copper precursor is reduced and carbon of the organic material is reduced,
Wherein when the copper precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, the copper of the copper precursor is oxidized and the carbon of the organic precursor is also oxidized. 3. The method of claim 2,
When the copper precursor-organic nanofibers are heat-treated in the atmosphere of the first oxygen partial pressure to the second partial pressure of oxygen, the carbon remaining in the copper precursor-organic nanofiber is oxidized and the residual carbon is removed from the structure of the copper- Lt; / RTI &gt;
When the copper precursor-organic nanofibers are heat-treated in an atmosphere having an oxygen partial pressure higher than the second oxygen partial pressure, the carbon remaining in the copper precursor-organic nanofiber is oxidized and the residual carbon remains in the structure of the copper-carbon nanofiber / RTI &gt; The method of claim 1, wherein the copper-carbon nanofibers are supported. The method according to claim 1,
Wherein the copper precursor comprises copper acetate (Cu (CH ₃ COO) ₂ ) and the organic material comprises a copper-carbon nanofiber including polyvinyl alcohol (PVA) forming a hydrogen bond with a copper precursor Gt; 5. The method of claim 4,
The step of forming the copper-carbon nanofibers by selectively oxidizing the copper precursor-organic nanofibers to oxidize the carbon of the organic material and simultaneously reduce the copper precursor to copper,
Carbon-nanofiber, comprising the step of autoclaving the copper precursor to copper from the acetate functionality of the copper precursor using the generated carbon monoxide (CO) as a reducing agent by the selective oxidation heat treatment. Way. The method according to claim 1,
The copper-carbon nanofiber is a structure in which the nanoparticles of copper are uniformly aggregated in the direction of the nanofibers in the nanofiber composed of carbon so as to prevent oxidation of copper,
Wherein the carbon nanofiber is formed from the organic material. The method according to claim 1,
The step of forming the copper-carbon nanofibers by selective oxidation treatment of the copper precursor-organic nanofibers may include decomposing a part of carbon constituting the copper precursor-organic nanofibers into combustion, not pyrolysis Carbon nanofibers. &Lt; Desc / Clms Page number 20 &gt; The method according to claim 1,
The step of forming the copper precursor-organic nanofiber including the copper precursor and the organic material
Providing a solution comprising the copper precursor, the organic material and a solvent; And
And forming the copper precursor-organic nanofibers from the solution by electrospinning using an electrostatic repulsion force formed by applying a high voltage to the solution. 9. A copper-carbon nanofiber formed by the manufacturing method according to any one of claims 1 to 8,
Copper nanoparticles are dispersed and arranged in an amorphous carbon matrix so as to prevent oxidation of copper,
Wherein the copper nanoparticles are arranged so as to have a relatively higher density in a core portion of the nanofiber while aggregating in a longitudinal direction of the nanofiber,
Copper-carbon nanofibers. 10. The method of claim 9,
Wherein the nanoparticles of copper disposed on the core portion of the nanofibers are arranged to be connected in the longitudinal direction of the nanofibers.

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