KR101984693B1 - Method for preparing reduced graphene oxide - Google Patents

Abstract

A method of electrochemically reducing graphene oxide is provided. Graphene oxide can be reduced at a normal temperature and a normal pressure in a short time.

Description

TECHNICAL FIELD The present invention relates to a method for preparing reduced graphene oxide,

The present invention relates to a method for producing reduced graphene oxide (RGO). And more particularly, to a method for producing electrochemically reduced graphene oxide.

Generally, graphite is a structure in which a plate-shaped two-dimensional graphene sheet in which carbon atoms are connected in a hexagonal shape is laminated. Recently graphene sheets of a layer or an aqueous layer were peeled off from graphite and the characteristics of the sheets were investigated. As a result, very useful properties different from those of conventional materials were found. The most notable feature is that when the electrons move in the graphene sheet, the electrons flow as if the mass of the electrons is zero, which means that the electrons flow at the rate at which the light travels in the vacuum, that is, the light flux.

The graphene sheet also has an unusual half-integer quantum Hall effect on electrons and holes. The mobility of the graphene sheet known to date has a high value of about 20,000 to 50,000 cm ² / Vs.

 There are micromechanical methods and SiC crystal pyrolysis methods as a method of producing graphene sheets. The micro-mechanical method is a method in which a scratched tape is attached to a graphite sample, and then the scratched tape is peeled off to obtain a graphene sheet which is separated from the graphite on the surface of the scratched tape. In this case, the number of the graphen sheets peeled out is not constant, and the shape is not uniform in the shape of the paper. Furthermore, it is impossible to obtain a graphene sheet with a large area. In the SiC crystal pyrolysis method, when the SiC single crystal is heated, the SiC on the surface is decomposed to remove Si, and the graphene sheet is formed by the remaining carbon (C). However, in the case of such a pyrolysis method, the SiC single crystal used as a starting material is very expensive, and it is very difficult to obtain a graphene sheet in a large area.

 In recent years, attempts have been made to manufacture graphene using a chemical method. For example, attempts have been made to remove graphite by chemical treatment. However, there are still difficulties in perfect control. Another method is to form and disperse graphene oxide and then reduce it. Graphene oxide is obtained by reacting carbon with an acid to contain an oxygen functional group such as a hydroxyl group, an epoxide group, a carboxyl group, and a lactate group.

As a method for reducing graphene oxide, a chemical reduction method or a reduction method by heat treatment is known. The chemical reduction method can be carried out by using various reducing agents such as hydrazine, NaBH ₄ , HI / AcOH, NaOH / KOH / NH ₃ , metal, phenylhydrazine and the like to obtain graphene having an electrical conductivity of several tens to several hundred S / cm. As a reduction method by heat treatment, graphene oxide is usually heat-treated at a high temperature (1,000 ° C or higher), and graphene having electric conductivity of 55,000 to 100,000 S / m is obtained. These methods are not preferable from the viewpoint of energy loss because the reaction time is long or is performed at a high temperature.

A problem to be solved by the present invention is to provide a method for producing reduced graphene oxide in a relatively short time at room temperature and atmospheric pressure.

According to an aspect of the present invention,

Forming a cathode by forming a graphene oxide layer on a conductive substrate;

Immersing the negative electrode and the positive electrode in an electrolytic solution containing a base; And

And reducing the graphene oxide by applying a voltage to the anode and the cathode. The present invention also provides a method for producing reduced graphene oxide.

According to an embodiment of the present invention, the applied voltage may be -0.3 to -1V.

According to another embodiment of the present invention, the base may be at least one selected from KOH, NaOH, Ba (OH) ₂ and Ca (OH) ₂ .

According to one embodiment of the present invention, reduced graphene oxide can be obtained at a normal temperature and a normal pressure in a short time.

1 is a schematic view showing the structure of a solar cell employing a transparent electrode including reduced graphene oxide according to an embodiment of the present invention.
2 is a UV-Vis spectrum of graphene according to Example 1 of the present invention and Comparative Examples 1 and 2.
3 is an IV graph of graphene according to Example 1 of the present invention and Comparative Examples 1 and 2;
4A to 4C show CV curves of graphene oxide according to Examples 1 to 3, respectively.

According to an aspect of the present invention, there is provided a method for preparing reduced graphene oxide, comprising: preparing a cathode by forming a graphene oxide layer on a conductive substrate; Immersing the negative electrode and the positive electrode in an electrolytic solution containing a base; And applying a voltage to the positive electrode and the negative electrode to reduce graphene oxide.

In the present invention, reduced graphene oxide can be produced in a short time at room temperature and atmospheric pressure by electrochemically reducing graphene oxide unlike conventional reduction by chemical reduction or heat treatment.

The term " graphen oxide " in the present specification is an oxide formed by oxidizing graphite. Since such graphene oxide can produce a dispersion solution unlike graphite, it can be thinned. Therefore, when graphene oxide is thinned using a dispersion solution of graphene oxide, and then the graphene oxide is reduced, it becomes possible to form graphene in sheet form. As used herein, the term " reduced graphene oxide " means a reduced material obtained by reducing such graphene oxide.

As used herein, the term " graphene " means a polycyclic aromatic molecule formed by covalent bonding of a plurality of carbon atoms, and the carbon atoms connected by the covalent bond form a 6-membered ring as a basic repeating unit, Or a 7-membered ring. The graphene thus appears to be a single layer of covalently bonded carbon atoms (usually sp ² bonds). The graphene may have various structures, and such a structure may vary depending on the content of the 5-membered ring and / or the 7-membered ring which may be contained in the graphene. The graphene may be formed of a single layer, but they may be stacked to form a plurality of layers, and a thickness of up to 100 nm may be formed. Typically, the side ends of the graphene are saturated with hydrogen atoms.

The reduced graphene oxide has a shape and physical properties similar to those of graphene as described above, but exhibits some different properties in terms of electrical properties and exhibits deteriorated properties in terms of conductivity in particular.

Such reduced graphene oxide does not have the complete form of graphene (C = C / C-C conjugated structure) and contains less C = C than graphene. That is, a variety of band gaps exist between the reducing graphene oxide and oxygen atoms or nitrogen atoms as a part other than carbon.

The step of forming a graphene oxide layer on a conductive substrate to produce a cathode may include first oxidizing the graphite to obtain graphene oxide.

Graphene oxide can be obtained, for example, by strong acid treatment of graphite (graphite). More specifically, graphene oxide can be produced by adding an oxidizing agent such as sulfuric acid and an oxidizing agent such as potassium permanganate to the graphite, heating and reacting, cooling to room temperature, and then oxidizing the graphite by adding an oxidizing agent such as hydrogen peroxide .

A solution containing the obtained graphene oxide may be applied on a conductive substrate and then dried to form a graphen oxide layer.

The conductive substrate may comprise a conductive metal or a graphene layer. When a conductive metal is included, a substrate made of a conductive metal may be used as it is. The conductive metal includes at least one metal selected from platinum, gold, silver and copper, or an alloy thereof.

When a graphene layer is included, it may be a graphene layer formed on a glass substrate or a plastic substrate. As the plastic substrate, polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN), polystyrene (PS)

Examples of the application process include spin coating, dip coating, spray coating, and the like.

The graphene layer may be formed by various methods. For example, the graphene layer may be formed by chemical vapor deposition (CVD). The graphene layer may be one layer to 100 layers. For example, from the first floor to the ten floor.

For example, a carbon source may be chemically deposited on a metal foil used as a graphitizing catalyst to form graphene, and then, on the graphene opposite to the side where the graphitization catalyst is formed, to transfer the graphene to the substrate, Polymer is spin-coated. Then, the graphite catalyst is removed using an etchant, the graphene on the PMMA is transferred to a glass substrate or a plastic substrate used for the cathode, and then the PMMA is removed using a solvent to produce a conductive substrate including the graphene layer .

In the graphene formation process, carbon can be supplied as a carbon source, and any material that can be present in a gaseous phase at a temperature of 300 ° C or higher can be used without any particular limitation. The gaseous carbon source may be a compound containing carbon. A compound having not more than 6 carbon atoms is preferable, a compound having not more than 4 carbon atoms is more preferable, and a compound having not more than 2 carbon atoms is more preferable. Examples thereof include at least one selected from the group consisting of carbon monoxide, methane, ethane, ethylene, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene and toluene .

Such a carbon source may be introduced into the chamber where the graphitizing catalyst is present at a constant pressure. In the chamber, the carbon source alone may be present, or may be present together with an inert gas such as helium, argon, or the like.

Hydrogen may be used in addition to the carbon source. Hydrogen may be used to keep the surface of the graphitization catalyst clean to control the gas phase reaction and may be used in an amount of 5 to 40% by volume of the total volume of the vessel, for example, 10 to 30% by volume, or 15 to 25% by volume .

After the carbon source is introduced into the chamber in which the graphitizing catalyst is present, the graphene is formed on the surface of the graphitizing catalyst by heat treatment at a predetermined temperature. The heat treatment is performed so as to maintain the film shape of the graphitizing catalyst. The heat treatment temperature serves as an important factor in the production of graphene, and may be, for example, 300 to 2000 占 폚, or 500 to 1500 占 폚. When the heat treatment temperature is within the above range, sheet-like graphene can be effectively obtained.

It is possible to control the degree of formation of graphene by maintaining the above-mentioned heat treatment at a predetermined temperature for a predetermined time. That is, when the heat treatment process is maintained for a long time, the number of graphenes formed increases, so that the thickness of the resulting graphene can be increased. If the heat treatment process is shorter than that, the resulting graphene thickness is reduced. Therefore, in order to obtain the desired graphene thickness, the holding time of the heat treatment process may be an important factor in addition to the type of the carbon source, the supply pressure, the type of the graphitizing catalyst, and the size of the chamber. The holding time of such a heat treatment process can be generally maintained for 0.001 to 1000 hours, and if desired, the desired graphene can be effectively obtained.

As the heat source for the heat treatment, induction heating, radiation heat, laser, IR, microwave, plasma, UV, surface plasmon heating and the like can be used without limitation. Such a heat source is attached to the chamber and functions to raise the temperature inside the chamber to a predetermined temperature.

After the heat treatment as described above, the heat treatment result is subjected to a predetermined cooling process. Such a cooling process is a process for uniformly growing the graphene so that it can be uniformly arranged. Rapid cooling may cause cracks or the like of the generated graphene. Therefore, it is preferable to cool gradually at a constant rate For example, at a rate of 10 to 100 ° C per minute, and it is also possible to use a method such as natural cooling. The natural cooling is obtained by simply removing the heat source used for the heat treatment, and it becomes possible to obtain a sufficient cooling rate even by removing the heat source.

The graphene obtained after such a cooling step may have a thickness ranging from 1 to 100 layers.

The heat treatment and cooling process as described above can be performed in one cycle, but it is possible to produce graphene having a dense structure with a high number of layers by repeating these processes several times.

When the conductive substrate includes a graphene layer, the current can smoothly flow and electrochemical reduction of graphene oxide can be facilitated.

The cathode used in the method for producing the reduced graphene oxide according to an embodiment of the present invention can use the cathode material generally used in the electrolytic apparatus without limitation. For example, one or more selected from carbon-based materials, platinum, iridium, stainless steel, carbon steel, gold, silver and copper. Examples of the carbon-based material include glassy carbon, graphite, and the like. Alternatively, at least one selected from lead oxide, platinum oxide, palladium oxide, iridium oxide, ruthenium oxide and manganese oxide may be used.

The method of preparing reduced graphene oxide according to an embodiment of the present invention is a method of reducing graphene oxide by using an electrolyte solution containing a base and reducing graphene oxide without causing graphene oxide layer to deteriorate, Can be continued.

The electrolyte containing the base may be an aqueous solution containing at least one base selected from KOH, NaOH, Ba (OH) ₂ and Ca (OH) ₂ . The base in the electrolytic solution may be present in a concentration of 0.1 to 1 mole. Effective reduction of graphene oxide can be achieved while reducing the damage to graphene oxide when the concentration is within this range.

The anode and cathode may be of any shape and size known in the art. For example, the anode and the cathode may be a flat type, a fiber type, or a mesh type having a plurality of holes.

The negative electrode and the positive electrode are prepared as described above and then immersed in an electrolytic solution containing a base. Then, a voltage is applied to the positive electrode and the negative electrode to reduce the graphene oxide. The applied voltage may be -0.3 to -1 V at this time. When it falls within the above range, the reduction reaction can be effectively performed without damaging the graphene oxide.

When the voltage is applied as described above, the various functional groups attached to the surface of the graphene oxide are reduced to form a double bond, thereby forming a sp ² bond like graphene. The degree of reduction of graphene oxide can be controlled by controlling the intensity and time of the applied voltage. Also, if a positive voltage is applied as needed, the reduced graphene oxide can be reversibly oxidized again.

According to one embodiment of the present invention, a reduced graphene oxide can be obtained in a short time at room temperature and at normal pressure. Also, since reduced graphene oxide can be produced in a large area and the thickness of the thin film can be freely adjusted by adjusting the concentration and spraying degree of the graphene oxide solution, the permeability can be easily controlled. In particular, since flexibility can be imparted, the transparent electrode can be easily handled and can be used in fields requiring transparent electrodes.

The transparent electrode comprising reduced graphene oxide prepared by the method according to one embodiment of the present invention can be manufactured by a conventional method. For example, in accordance with an embodiment of the present invention, the reduced graphene oxide formed on a conductive substrate such as a conductive metal is washed with deionized water, and then the PMMA is coated on the reduced graphene oxide layer. Then, the conductive metal substrate is removed with aqua regia, the reduced graphene oxide layer coated with PMMA is transferred to the transparent substrate, and then the transparent electrode is manufactured by removing the PMMA.

Examples of the field in which the transparent electrode including reduced graphene oxide is utilized include various display devices such as a liquid crystal display device, an electronic paper display device, and an organic light emitting display device, and are useful for a battery field, for example, Can be used to

As described above, when the transparent electrode is used for the display element, the display element can be bent freely and convenience is increased. In the case of a solar cell, when the transparent electrode according to the present invention is used, So that it is possible to use the light efficiently, and it becomes possible to improve the light efficiency.

When a transparent electrode including reduced graphene oxide according to an embodiment of the present invention is used for various devices, the thickness of the transparent electrode is preferably adjusted in consideration of transparency. For example, when the thickness of the transparent electrode is more than 200 nm, the transparency may be lowered and the light efficiency may be poor. When the thickness is less than 0.1 nm, the sheet resistance may be too low It may be undesirably low or the film may be uneven.

An example of a solar cell employing a transparent electrode including reduced graphene oxide according to an embodiment of the present invention is a dye-sensitized solar cell as shown in FIG. 1, wherein the dye-sensitized solar cell includes a semiconductor electrode 10, Wherein the semiconductor electrode comprises a conductive transparent substrate (11) and a light absorbing layer (12), and a colloidal solution of the nanoparticle oxide (12a) on the conductive transparent substrate Coating is performed, heating is performed in a high-temperature electric furnace, and the dye 12b is adsorbed.

The transparent electrode is used as the conductive transparent substrate 11. The transparent electrode is obtained by transferring the reduced graphene oxide onto a transparent substrate. As the transparent substrate, for example, a transparent polymer material such as polyethylene terephthalate, polycarbonate, polyimide, or polyethylene naphthalate, or a glass substrate Can be used. This is applied to the counter electrode 14 as it is.

In order to form a structure capable of bending the dye-sensitized solar cell, for example, a cylindrical structure, it is preferable that all of the transparent electrodes, the counter electrodes, and the like are made flexible together.

The nanoparticle oxide 12a used in the solar cell is preferably an n-type semiconductor which serves as a semiconductor fine particle, and under the photoexcitation, the conduction band electrons serve as a carrier and provide an anode current. Specific examples thereof include TiO ₂ , SnO ₂ , ZnO ₂ , WO ₃ , Nb ₂ O ₅ , Al ₂ O ₃ , MgO, and TiSrO ₃ , and particularly preferred is anatase TiO ₂ . The metal oxides are not limited to these, and they may be used alone or in combination of two or more thereof. It is preferable that the semiconductor particulates have a large surface area in order to allow the dye adsorbed on the surface to absorb more light. For this purpose, it is preferable that the particle diameter of the semiconductor fine particles is about 20 nm or less.

The dye (12b) can be used without limitation as long as it is generally used in the field of solar cells or photovoltaic cells, but a ruthenium complex is preferable. As the ruthenium complex, RuL ₂ (SCN) ₂ , RuL ₂ (H ₂ O) ₂ , RuL ₃ , RuL ₂ and the like can be used. (Wherein L is 2,2'-bipyridyl-4,4'- And the like. However, such a dye (12b) is not particularly limited as long as it has a charge-separating function and exhibits a sensitizing action. In addition to the ruthenium complex, a dye such as rhodamine B, rose bengal, eosin, erythrosine, , Cryptoxanthin, and the like, basic dyes such as phenosapranin, carbide blue, thiosine and methylene blue, porphyrin compounds such as chlorophyll, zinc porphyrin and magnesium porphyrin, other azo dyes, phthalocyanine compounds, Ru Trisbipyridyl and the like, anthraquinone-based coloring matters, and polycyclic quinone-based coloring matters, and these may be used singly or in combination of two or more.

The thickness of the light absorbing layer 12 including the nano-particle oxide 12a and the dye 12b is 15 占 퐉 or less, preferably 1 to 15 占 퐉. This is because the light absorption layer has a large series resistance for its structural reasons and an increase in series resistance results in a reduction in conversion efficiency. By keeping the film thickness to 15 mu m or less, Can be prevented from being lowered.

The electrolyte layer 13 used in the dye-sensitized solar cell may be a liquid electrolyte, an ionic liquid electrolyte, an ionic gel electrolyte, a polymer electrolyte, or a complex thereof. Typically, it is made of an electrolytic solution, and includes the light absorbing layer 12, or the electrolyte is formed to infiltrate the light absorbing layer. As the electrolytic solution, for example, an acetonitrile solution of iodine or the like can be used, but not limited thereto, and any electrolytic solution having a hole conduction function can be used without limitation.

In addition, the dye-sensitized solar cell may further include a catalyst layer. The catalyst layer is for promoting the redox reaction of the dye-sensitized solar cell, and may be formed of platinum, carbon, graphite, carbon nanotubes, carbon black, A complex among them, and the like, which are located between the electrolyte layer and the counter electrode. It is preferable that the catalyst layer has a fine structure with an increased surface area. For example, if the catalyst layer is platinum, it is preferable that the catalyst layer is in a platinum black state and the carbon layer is in a porous state. The platinum black state can be formed by the anodic oxidation of platinum, the treatment with chloroplatinic acid, or the like, and the porous carbon can be formed by a method such as sintering of carbon microparticles or firing of an organic polymer.

The above-described dye-sensitized solar cell has excellent optical efficiency and processability by employing transparent electrode containing reduced graphene oxide which is excellent in conductivity.

Examples of the display device using the transparent electrode including the reduced graphene oxide include an electronic paper display device, an organic light emitting display device, and a liquid crystal display device. Among these organic light emitting display devices, the organic light emitting display device is an active light emitting display device that uses a phenomenon in which light is generated while electrons and holes are combined in an organic film when a current is supplied to a fluorescent or phosphorescent organic compound thin film. A typical organic electroluminescent device has a structure in which an anode is formed on a substrate, and a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are sequentially formed on the anode. In order to facilitate injection of electrons and holes, an electron injection layer and a hole injection layer may be further provided. If necessary, a hole blocking layer, a buffer layer, and the like may be further provided. The anode is preferably a transparent and excellent conductive material, and the transparent electrode containing the reduced graphene oxide according to an embodiment of the present invention can be advantageously used.

As a material of the hole transporting layer, a commonly used material may be used, and polytriphenylamine may be preferably used, but the present invention is not limited thereto.

As the material of the electron transporting layer, a commonly used material can be used, and preferably polyoxadiazole can be used, but the present invention is not limited thereto.

As the luminescent material used in the luminescent layer, fluorescent or phosphorescent materials generally used may be used without limitation, but they may be selected from the group consisting of at least one polymer host, a mixture host of a polymer and a small molecule, a low molecular host, and a non-luminescent polymer matrix And may further include one or more. Here, the polymer host, the low molecular weight host, and the non-light emitting polymer matrix may be any of those conventionally used for forming the light emitting layer for the organic electroluminescent device. Examples of the polymer host include poly (vinylcarbazole), polyfluorene, poly (p-phenylenevinylene), polythiophene and the like. Examples of the low molecular weight host include CBP (4,4'-N, N'-dicarbazole-biphenyl), 4,4'- (3,6-biphenylcarbazolyl)] - 1-1, 1'-biphenyl {4,4'-bis [9- Biphenyl}, 9,10-bis [(2 ', 7'-t-butyl) -9', 9 "-spirobifluorenyl anthracene, tetrafluorene, But are not limited to, polymethyl methacrylate and polystyrene. The above-described light emitting layer can be formed by a vacuum deposition method, a sputtering method, a printing method, a coating method, an inkjet method, or the like.

The fabrication of the organic electroluminescent device according to one embodiment of the present invention does not require a special device or method and can be manufactured according to a method of fabricating an organic electroluminescent device using a conventional light emitting material.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

Example 1

Preparation of graphene oxide

1 mg of pure graphite (purity 99.999%, -200 mesh, manufactured by Alfa Aesar), 20 ml of fuming nitric acid and 8.5 mg of sodium chloride oxide were mixed at room temperature. The mixture was stirred for 24 hours and then washed, filtered and cleaned to prepare graphene oxide.

Cathode manufacturing

A Cu foil (Alfa Aesar thickness: 125 占 퐉) was placed in a self-made heating CVD chamber and heated at 1000 占 폚 for 30 minutes using a halogen lamp heat source while hydrogen gas was constantly introduced into the chamber at 200 sccm. And a mixed gas of CH _{4 20} sccm / H _{2 4} sccm was added to the chamber for 30 minutes. The chamber was then slowly cooled to grow graphene uniformly to form a graphene monolayer having a thickness of 10 mm x 10 mm with a thickness of one layer.

Subsequently, to separate the graphene from the Cu foil, a solution of chlorobenzene (5 wt%) in which PMMA was dissolved on a graphene / Cu foil was coated at a rate of 1,000 rpm for 60 seconds, and the resultant was subjected to Cu etch (FeCl ₃ ) Solution (Transene type 1). And the Cu foil was removed by immersing for 1 hour to separate the graphene attached to the PMMA. The graphene attached to the PMMA was transferred to a glass substrate, dried, and then PMMA was removed with acetone.

2 mg of the graphene oxide prepared above was placed in 20 ml of DI wafer and the pH was adjusted to> 7 with NaOH and sonicated for 2 hours. 200 占 퐇 of the aqueous solution thus formed was sprayed onto the graphene layer formed on the glass substrate to prepare a negative electrode.

For the reduction of graphene oxide, glassy carbon was used as an anode, Ag / AgCl was used as a reference electrode, and 0.1 M KOH aqueous solution was used as an electrolyte solution.

A voltage of -1 V was applied to the positive electrode and the negative electrode for 400 s.

Examples 2 to 3

Graphene oxide was reduced in the same manner as in Example 1, except that 0.5M and 1M of KOH aqueous solution were used instead of 0.1M KOH aqueous solution, respectively.

Comparative Example 1

Graphene oxide was reduced in the same manner as in Example 1, except that 0.1 M H ₂ SO ₄ aqueous solution instead of 0.1 M KOH was used as an electrolyte and a voltage of -0.7 V was applied for 200 seconds.

Comparative Example 2

0.005 g of the graphene oxide powder synthesized in Example 1 was put into 50 ml of deionized water and dispersed by ultrasonication for 30 minutes and then centrifuged at 4000 rpm for 40 minutes to remove microparticulate graphene oxide. 50 μl of hydrazine (N ₂ H ₄ ) solution was added to 200 ml of the resulting graphene oxide solution, stirred at 100 ° C for 12 hours, and then cooled to room temperature. Thus, reduced graphene oxide was obtained.

UV-Vis spectra and I-V curves of the reduced graphene oxide obtained in Example 1 and Comparative Examples 1 and 2 are shown in Fig. 2 and Fig. 3, respectively. The UV-Vis spectra were measured using a Shinko (S-3100) and I-V curves were obtained using a MS-Teck (Model-5500) and a Hewlett Packard (4145B Semiconductor Analyzer) probe station. The I-V curve was measured at an interval of about 2 mm using two probes.

For comparison, graphene oxide and graphene produced by the CVD method are shown together with the UV-Vis spectrum and the I-V curve. As graphene oxide, graphene oxide obtained by the same method as in Example 1 was used, and graphene produced by the CVD method was obtained as follows.

A Cu foil (Alfa Aeser thickness: 125 占 퐉) was placed in a self-made heated CVD chamber and heated at 1000 占 폚 for 30 minutes using a halogen lamp heat source while hydrogen gas was constantly introduced into the chamber at 200 sccm . And a mixed gas of CH _{4 20} sccm / H _{2 4} sccm was added to the chamber for 30 minutes. The chamber was then slowly cooled to grow graphene uniformly to form a graphene monolayer having a thickness of 10 mm x 10 mm with a thickness of one layer.

Subsequently, to separate the graphene from the Cu foil, a chlorobenzene solution (5% by weight) in which PMMA was dissolved on a graphene / Cu foil was coated at a rate of 1,000 rpm for 60 seconds and then the resultant was treated with a Cu ethene solution 1). And the Cu foil was removed by immersing for 1 hour to separate the graphene attached to the PMMA. The graphene attached to the PMMA was transferred to a glass substrate, dried, and then PMMA was removed with acetone.

As shown in FIG. 2, the reduced graphene oxide according to an embodiment of the present invention has a lower transmittance than that of the graphene oxide and has a lower transmittance than the reduced graphene oxide of Comparative Example 1 and Comparative Example 2. That is, when the reduction reaction of graphene oxide having good permeability is proceeded, the transmittance is decreased as shown in FIG. The transmittance of the reduced graphene oxide of Example 1 was about 92%, and the reduced graphene oxide of Comparative Example 2 was about 95%. From this, it can be seen that the reduction of graphene oxide was effectively performed by the method of producing reduced graphene oxide according to an embodiment of the present invention.

Meanwhile, as shown in FIG. 3, reduced graphene oxide according to an embodiment of the present invention has increased electrical conductivity compared to graphene oxide. The chemically reduced graphene oxide of Comparative Example 2 showed a resistance of about 30 kΩ while the electrochemically reduced graphene oxide of the electrolyte containing the base according to Example 1 of the present invention exhibited a resistance of about 9.5 kΩ , The electrochemically reduced graphene oxide in the electrolytic solution containing the acid according to Comparative Example 1 showed a resistance of about 17.9 k ?. From this, it can be seen that reducing graphene oxide by the method according to one embodiment of the present invention effectively forms reduced graphene oxide.

4A to 4C show the CV curves of the graphene oxides of Examples 1 to 3, respectively. As shown in FIG. 4, reduction of reduced graphene oxide can be confirmed by the electrochemical methods of Examples 1 to 3.

Example 6: Production of solar cell

A titanium oxide particle paste having a particle size of about 7 to 25 nm was coated on a transparent electrode containing the reduced graphene oxide obtained in Example 1 and applied to an area of 1 cm ² , and a low temperature firing process (150 ° C or less) A porous titanium oxide film having a thickness of 탆 was prepared. Then, dye adsorption treatment was carried out for more than 12 hours on 0.3 mM Ru (4,4'-dicarboxy-2,2'-bipyridine) ₂ (NCS) ₂ solution dissolved in ethanol at room temperature. After that, the porous titanium oxide film on which the dye was adsorbed was washed with ethanol and dried at room temperature to produce a photocathode.

As the counter electrode, a Pt reduction electrode was deposited using a sputter on the transparent electrode including the reduced graphene oxide obtained in Example 1, and a micro hole was formed using a drill having a diameter of 0.75 mm to inject the electrolyte, Respectively.

A thermoplastic polymer film having a thickness of 60 탆 was sandwiched between the photo negative electrode and the counter electrode at 100 캜 for 9 seconds to bond the two electrodes. The dye-sensitized solar cell was fabricated by injecting an oxidation-reduction electrolyte through fine holes formed in the counter electrode and blocking fine holes using a cover glass and a thermoplastic polymer film. The oxidation-reduction electrolyte used was 21.928 g of tetrapropylammonium iodide and 1.931 g of I ₂ in a solvent composed of 80% of ethylene carbonate and 20% of acetonitrile Was used.

Example 7: Fabrication of organic electroluminescent device

The reduced graphene oxide obtained in Example 1 was transferred to a glass substrate to obtain a transparent electrode. An electrode pattern was formed on the transparent electrode and cleaned. PEDOT was coated on the thus-cleaned transparent electrode to a thickness of about 50 nm and then baked at 120 ° C for about 5 minutes to form a hole injection layer.

Green 223 polymer was spin-coated on the hole injection layer above the hole injection layer, baked at 100 ° C for 1 hour, and the solvent was completely removed in a vacuum oven to form a light emitting layer with a thickness of 80 nm / RTI >

Subsequently, Alq ₃ was vacuum-deposited on the polymer luminescent layer at a rate of 1.0 Å / sec while maintaining the degree of vacuum below 4 × 10 ^-6 torr using a vacuum evaporator to form an electron transport layer having a thickness of 30 nm, LiF was vacuum deposited at a rate of 0.1 A / sec to form an electron injection layer with a thickness of 5 nm.

 Then, Al was deposited at a rate of 10 A / sec to deposit a cathode having a thickness of 200 nm and encapsulation, thereby completing an organic electroluminescent device. At this time, the sealing process was performed by putting BaO powder in a glove box under a dry nitrogen gas atmosphere, sealing with a metal can, and then finishing with a UV curing agent.

Claims (10)

Forming a cathode by forming a graphene oxide layer on a conductive substrate;
Immersing the negative electrode and the positive electrode in an electrolytic solution containing a base; And
And applying a voltage to the positive and negative electrodes to reduce graphene oxide
Method for the preparation of reduced graphene oxide. The method according to claim 1,
Wherein the anode is at least one selected from a carbon-based material, platinum, iridium, stainless steel, carbon steel, gold, silver and copper. The method according to claim 1,
Wherein the anode is at least one selected from the group consisting of lead oxide, platinum oxide, palladium oxide, iridium oxide, ruthenium oxide and manganese oxide. 3. The method of claim 2,
Wherein the carbon-based material is glassy carbon or graphite. The method according to claim 2, wherein
Wherein the conductive substrate comprises a conductive metal or graphene layer. 6. The method of claim 5,
Wherein the conductive metal is at least one selected from platinum, gold, silver and copper. 6. The method of claim 5,
Wherein the graphene layer is one to ten layers. The method according to claim 1,
Wherein the base is at least one of KOH, NaOH, Ba (OH) ₂ and Ca (OH) ₂ . The method according to claim 1,
Wherein the base is contained in a concentration of 0.1 to 1 mole. The method according to claim 1,
And a voltage of -0.3 to -1 V is applied.

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