KR101717911B1 - Manufacturing method of electrodeposited ZnO nanorod on carbon nanofiber and electrodes comprising the carbon nanofiber therefrom - Google Patents

Abstract

The present invention relates to a method for manufacturing a carbon nanofiber on which a zinc oxide nanorod has grown and, more particularly, to a method including: a) a step of preparing a mixed solution by stirring polyacrylonitrile (PAN) polymer-added N,N-dimethylformamide (DMF); b) a step of preparing a polymer nanofiber by performing electrospinning on the mixed solution; c) a step of manufacturing the carbon nanofiber by calcining the polymer nanofiber at 500 to 2,000 degrees Celsius; and d) a step of growing the zinc oxide nanorod on the carbon nanofiber by electrochemical deposition, wherein the shape of a terminal end part of the zinc oxide nanorod is adjustable by electrochemical deposition. Further, the present invention relates to the carbon nanofiber on which the zinc oxide nanorod has grown that is manufactured by the same, and an electrode and a photoelectrochemical battery using the same.

Description

[0001] The present invention relates to a method of manufacturing carbon nanofibers grown from zinc oxide nanorods by electrochemical deposition, and to an electrode comprising carbon nanofibers prepared therefrom,

The present invention provides a method for manufacturing carbon nanofibers grown with zinc oxide nanorods capable of controlling the shape of a terminal portion through an electrochemical deposition method and an electrode using the carbon nanofibers prepared therefrom.

The present invention provides a carbon nanofiber in which zinc oxide nanorods capable of regulating the shape of a terminal portion by electrochemical deposition are suitable for hydrogen production using water decomposition process through irradiation of sunlight.

Zinc oxide is a semiconductor material having an energy band gap of 3.37 eV and is utilized in solar cells, piezoelectric devices, gas sensors, super capacitors, and lithium ion battery electrodes. A key element in the technology of hydrogen production through water degradation by irradiating sunlight is the quantum efficiency of the semiconductor material and the lifetime of the photoexcited electron. The zinc oxide has a low quantum efficiency and a long lifetime It is difficult to utilize the zinc oxide alone in the hydrogen production part using the water decomposition process through the irradiation of sunlight. In order to solve this problem, the inventors of the present invention prepared nanotubes of zinc oxide on the surface of carbon nanofibers by electrochemical deposition method by adjusting terminal shape and then used it as an electrode for hydrogen production to irradiate sunlight in an aqueous solution Hydrogen production using water was applied to hydrogen production.

The following techniques are available for growing conventional zinc oxide on carbon nanofibers. Korean Patent Laid-Open No. 10-2013-0067870 grows zinc oxide nano-rods on carbon fibers by electroless plating. Here, the role of zinc oxide is focused on improving the strength of the carbon fiber and is not related to the electrode material for hydrogen production. Also, Korean Patent Laid-Open No. 10-2010-0086592 discloses a method of manufacturing a zinc oxide rod by hydrothermal synthesis And how to do it. However, there is a disadvantage in that a manufacturing step is complicated because a photoresist pattern is necessary when manufacturing a nano rod.

The zinc oxide produced by this method has a disadvantage in that the distribution is not uniform and the shape control is relatively difficult. In order to solve this problem, the inventors of the present invention prepared carbon nanofibers grown with zinc oxide nanorods that can be controlled in shape through electrochemical deposition by a relatively simple process, And to propose a method to utilize it in the production of hydrogen using the water decomposition process through solar irradiation.

Korean Patent Publication No. 2013-0067870 Korea Patent Publication No. 2010-0086592

In order to solve the above problems, the present invention relates to a method for producing carbon nanofibers grown with zinc oxide nanorods capable of utilizing both the specific surface area and electrical characteristics of carbon fibers and the catalytic activity of zinc oxide ≪ / RTI >

In addition, according to the present invention, zinc oxide is uniformly deposited on carbon nanofibers according to the above method, and the end portion shape of the zinc oxide nano-rod is easily controlled. Thus, And to increase production efficiency.

A method for producing a carbon nanofiber in which a zinc oxide nano-rod of the present invention is grown comprises the steps of: a) preparing a mixed solution by adding a polyacronitrile (PAN) polymer to N, N-dimethylformamide (DMF) and stirring the mixture; b) electrospinning the mixed solution to produce a polymer nanofiber; c) firing the polymer nanofibers at 500 to 2000 占 폚 to produce carbon nanofibers; And d) growing zinc oxide nanorods on the carbon nanofibers through electrochemical deposition.

According to one embodiment of the production process of the present invention, the mixed solution of step a) may comprise 5 to 20% by weight of PAN, based on the total weight.

According to an embodiment of the manufacturing method of the present invention, a voltage of 5 to 100 kV may be applied during the electrospinning of step b).

According to one embodiment of the production method of the present invention, the polymer nanofibers of step c) can be calcined at 500 ° C to 1500 ° C.

According to one embodiment of the production method of the present invention, the firing of the polymer nanofibers can be performed for 1 to 4 hours.

According to one embodiment of the production process of the present invention, step d) can be carried out at 50 캜 to 80 캜.

According to one embodiment of the production process of the present invention, zinc acetate, zinc chloride or zinc nitrate may be used as a precursor of zinc oxide in step d).

According to one embodiment of the present invention, the zinc oxide precursor may be used at a concentration of 0.1 mM to 5 mM.

According to one embodiment of the production method of the present invention, potassium chloride may be used as an electrolyte in performing electrochemical deposition in step d).

According to an embodiment of the present invention, the concentration of the potassium chloride may be 0.1 mM to 0.5 mM.

According to an embodiment of the manufacturing method of the present invention, the electrochemical deposition method may be performed by applying a voltage of 1 V to 20 V in step d).

According to one embodiment of the production process of the present invention, step d) can be carried out for 15 minutes to 5 hours.

The electrode of the present invention uses the carbon nanofibers on which the zinc oxide nano-rods grown according to the manufacturing method of the present invention described above are grown.

According to one embodiment of the electrode of the present invention, the zinc oxide nanorods may have a length of 100 nm to 1 占 퐉.

According to one embodiment of the electrode of the present invention, the diameter of the zinc oxide nano-rods may range from 20 nm to 300 nm.

According to one embodiment of the electrode of the present invention, the length of the carbon nanofibers may range from 100 nm to 10 mu m.

According to one embodiment of the electrode of the present invention, the diameter of the carbon nanofibers may range from 50 nm to 2 [mu] m.

According to one embodiment of the electrode of the present invention, the aspect ratio of the carbon nanofibers may range from 2 to 100. [

According to one embodiment of the electrode of the present invention, the terminal portion of the zinc oxide nano-rod may be concave or convex.

The photoelectrochemical cell of the present invention includes the above-described electrode, electrolyte, and counter electrode of the present invention.

The production process according to the present invention is simpler than the conventional hydrothermal synthesis method, and the shape and length of zinc oxide can be relatively easily controlled. In addition, the carbon nanofibers grown with zinc oxide nanorods by the electrochemical vapor deposition method have a large specific surface area and electric characteristics possessed by the conventional zinc oxide particles, Zinc nanorods can additionally utilize catalytic activity.

Further, according to the present invention, it is possible to manufacture carbon nanofibers grown with zinc oxide nanorods which do not require expensive equipment and can control the shape of the terminal portions by a relatively simple process, It can be used for hydrogen production using water decomposition process through solar irradiation.

1 is an SEM photograph of a carbon nanofiber grown with zinc oxide nanorods prepared by the method of Example 1 of the present invention.
2 is an EDX photograph of a carbon nanofiber grown with zinc oxide nanorods prepared by the method of Example 1 of the present invention.
3 is an SEM photograph of a carbon nanofiber grown with zinc oxide nanorods prepared by the method of Example 2 of the present invention.
4 is an EDX photograph of a carbon nanofiber grown with zinc oxide nanorods prepared by the method of Example 2 of the present invention.
FIG. 5 is an X-ray diffraction (XRD) graph of carbon nanofibers and carbon nanofibers grown with zinc oxide nanorods prepared by the methods of Example 1, Example 2, and Comparative Example 1 of the present invention.
FIG. 6 is a graph showing the results of the water decomposition process using the carbon nanofibers grown by the zinc oxide nano-rods prepared by the methods of Examples 1 and 2 and Comparative Example 1, FIG. 2 is a graph showing the amount of hydrogen generated by the hydrogen generator according to time. FIG.
FIG. 7 is a graph showing the results of the water decomposition process by the irradiation of sunlight when the carbon nanofibers grown by the zinc oxide nano-rods prepared by the methods of Example 1, Example 2, and Comparative Example 1 of the present invention were used as electrodes for hydrogen production And the hydrogen production rate is shown in FIG.
FIG. 8 is a diagram illustrating the end portions of the zinc oxide nano-rods produced by Example 1 (left) and Example 2 (right) of the present invention. FIG.
9 is a graph of nitrogen adsorption / desorption curves of Example 1, Example 2, and Comparative Example 1 of the present invention.
10 is a Kubelka munk function conversion graph showing the band gap energies of the first, second and comparative examples of the present invention.

One embodiment of the present invention provides a method for producing carbon nanofibers grown with zinc oxide nanorods. Hereinafter, this will be described in more detail.

The method for producing the carbon nanofibers grown with the zinc oxide nanorod includes the following steps.

a) preparing a mixed solution by adding a polyacronitrile (PAN) polymer to N, N-dimethylformamide (DMF) and stirring;

b) electrospinning the mixed solution to produce a polymer nanofiber;

c) firing the polymer nanofibers at 500 to 2000 占 폚 to produce carbon nanofibers; And

d) growing zinc oxide nanorods on the carbon nanofibers through electrochemical deposition.

The steps are generally divided into a step (a) of producing an electrospinning solution, a step (b) of producing a polymer nanofiber, a step (c) of producing a carbon nanofiber, and a step (Step d). ≪ / RTI >

Manufacture of Electrospray Solutions

First, an electrolytic solution is prepared to prepare polymer nanofibers. In an embodiment of the present invention, the electrolytic solution may be a mixed solution obtained by adding a polyacronitrile (PAN) polymer to N, N-dimethylformamide (DMF) and stirring. The mixed solution may contain about 5 to 20 wt% of PAN, preferably about 10 to 15 wt% of PAN, based on the total weight.

In one embodiment of the present invention, 1 part by weight of PAN was added to 9 parts by weight of DMF, and the mixture was stirred at 60 DEG C for 4 hours and then stirred at room temperature for 12 hours to prepare a 10% by weight PAN solution. , A light brown PAN / DMF mixed solution can be prepared.

Manufacture of Polymer Nanofibers

The obtained mixed solution is spun using an electrospinning apparatus to produce polymer nanofibers. The commercial electrospinning apparatus can be composed of a spinning nozzle connected to a metering pump capable of quantitatively injecting a spinning solution, a high voltage generator, and an electrode for forming a spun fiber layer. A grounded metal plate is used as the negative electrode, and a spinning nozzle equipped with a pump whose discharge rate is adjusted per hour is used as an anode. The polymer nanofiber having a diameter of about 700 to 900 nm can be prepared by adjusting the solution discharge rate and the voltage to about 5 to 100 kV and the discharge rate to about 10 to 200 μl / min.

Manufacture of carbon nanofibers

The obtained polymer nanofiber is heat-treated to obtain carbon nanofibers. In one embodiment of the present invention, the firing of the polymer nanofibers is performed at about 500 to 2000 ° C, preferably about 500 to 1500 ° C, more preferably about 600 to 1400 ° C, under a nitrogen atmosphere . The firing can be carried out for about 1 to 4 hours. In an embodiment of the present invention, the diameter of the carbon nanofibers may be about 50 nm to 2 μm. In one embodiment of the present invention, the length of the carbon nanofibers may be about 50 nm to 10 mu m, or preferably about 100 nm to 2 mu m. The aspect ratio of the carbon nanofibers is in the range of 2 to 100.

Zinc oxide which can control the shape of the terminal part by electrochemical vapor deposition Nanorod  Fabrication of grown carbon nanofibers

Zinc oxide nanorods capable of controlling the morphology can be grown on the surface of the obtained carbon nanofibers by electrochemical deposition.

The hydrogen production efficiency can be remarkably increased by controlling the shape of the terminal portion of the zinc oxide nano-rod. Specifically, by controlling the light absorption rate depending on the shape of the terminal portion, the hydrogen production rate and the like can be controlled, have. The shape of the end portion can be concave or convex as shown in FIG. 8, and when the end portion has a concave end portion, the energy band gap is small, so that more light can be absorbed and thus hydrogen generation efficiency can be further improved.

The end portion shape control of the zinc oxide nano-rods can be realized through the components of the growth solution, their concentration, the process conditions of the electrochemical deposition method, and the like.

In the electrochemical deposition, a sample is placed in a growth solution and an electric field is applied at a low temperature of about 50 ° C to 80 ° C to chemically synthesize a vertically aligned one-dimensional nanostructure in a relatively short time. Electrochemical deposition is achieved using a three electrode system. The three-electrode system is composed of a reference electrode, a counter electrode, and a working electrode. The precursor of the metal to be deposited is added to the electrolyte and the aqueous solution, and electrochemical deposition can be performed on the sample by applying a constant voltage or current to the electrolyte. As the electrolyte, potassium chloride and the like may be used.

In one embodiment of the present invention, as the precursor of zinc oxide, zinc acetate, zinc chloride, zinc nitrate, or the like may be used for the growth solution. In one embodiment of the invention, the concentration of zinc oxide during electrochemical deposition may be from about 0.1 mM to 5 mM, preferably from about 0.25 mM to 0.5 mM. In one embodiment of the invention, the electrochemical deposition time is from about 15 minutes to 5 hours, preferably from 30 minutes to 3 hours. The electrochemical deposition is performed in an electric field of -1 V to -20 V applied. The length of the zinc oxide produced in one embodiment of the invention can also be about 100 nm to 1 μm, preferably about 450 nm to 500 nm. The diameter of the zinc oxide nanorod may range from about 20 nm to 300 nm.

Another embodiment of the present invention provides an electrode and a cell using the carbon nanofibers grown by the zinc oxide nano-rods produced by the above method, and they are used for production of hydrogen through electrolysis of water in the field of solar energy conversion .

Particularly, the present invention has a hydrogen production efficiency of 2 to 4 times or more as compared with zinc oxide nanoparticles used as a conventional photocatalyst by depositing zinc oxide capable of controlling the morphology on carbon nanofibers. In addition, the rate of hydrogen generation is much faster because of the high electrical conductivity and adsorption of the carbon nanofibers and the shape of the end portions of the zinc oxide nanorods.

Example :

Example  One

A mixed solution prepared by adding 1 part by weight of polyacrylonitrile (PAN) to 9 parts by weight of N, N-dimethylformamide (DMF) was stirred at a temperature of 60 ° C for 24 hours at 300 rpm and mixed. The prepared brown colloid mixture was electrospun using a 27 gauge syringe needle under the conditions of a voltage of 20 kV and a spinning speed of 50 l / min. After the spinning, it was left at room temperature for 24 hours. The prepared PAN fibers were heated at a rate of 5 ° C / min in an atmospheric state and maintained at 250 ° C for 20 minutes. And then maintained at 250 DEG C for 10 minutes in a nitrogen atmosphere. Thereafter, the temperature was raised to 750 ° C at a rate of 5 ° C / min and then maintained at 750 ° C for 1 hour. Finally, the temperature was increased from 1400 ° C to 5 ° C / min, and the temperature was maintained at 1400 ° C for 1 hour, followed by cooling at room temperature.

The carbon nanofibers obtained were cut into a predetermined size (1 cm x 3 cm) and then electrochemically deposited using a zinc acetate solution (0.25 mM, 50 mL). The reference electrode was Ag / AgCl, the counter electrode was Pt wire, the working electrode was used as the carbon nanofiber prepared above, and the electrolyte was KCl solution (0.1 mM). The solution was maintained at 60 ° C for 10 minutes using a water bath, maintained at -1 V against the reference electrode for 30 minutes, dried at 80 ° C for 6 hours, and dried at 400 ° C for 30 minutes to obtain a carbon nanofiber .

Fig. 1 is an electron microscope (SEM) photograph of the carbon nanofibers prepared in Example 1. Fig. The zinc oxide nanorods form a concave nanorod with a length of about 457 ± 5 nm.

FIG. 2 is an EDX photograph of the carbon nanofiber grown with the zinc oxide nanorod prepared by the method of Example 1, and it was confirmed that the zinc oxide is evenly distributed on the surface of the carbon nanofiber.

From FIG. 5, it was confirmed that the crystal form of the zinc oxide nano-rod having the concave end formed in Example 1 had a hexagonal system structure.

From FIG. 9, it was confirmed that the specific surface area of the carbon nanofiber having the concave zinc oxide nanorod grown in Example 1 was 12.43 m ² / g.

10, it was confirmed that the size of the energy band gap of the carbon nanofiber having the concave zinc oxide nanorod grown in Example 1 was 3.04 eV.

Example  2

Carbon nanofibers grown with zinc oxide nanorods were obtained in the same manner as in Example 1 except that the concentration of the zinc acetate solution was changed to 0.50 mM and 50 mL.

Fig. 3 is an electron microscope (SEM) photograph of the carbon nanofibers prepared in Example 2. Fig. The zinc oxide nanorods form a convex nano-rod with a length of about 492 ± 5 nm.

Compared with Example 1, it had a longer, thicker, and dense structure. This is because the concentration of the zinc precursor is so high that the formation of seed which helps in the formation of ZnO occurs more easily on the surface of the carbon nanofibers.

FIG. 4 is an EDX image of the carbon nanofiber grown with the zinc oxide nanorod prepared by the method of Example 2, and it was confirmed that zinc oxide is evenly distributed on the surface of the carbon nanofiber.

From FIG. 5, it was confirmed that the crystalline form of the zinc oxide nanorod having the convex shape formed in Example 2 had a hexagonal system structure.

From FIG. 9, it was confirmed that the specific surface area of the carbon nanofiber having the concave zinc oxide nanorod grown in Example 1 was 12.43 m ² / g.

10, it was confirmed that the size of the energy band gap of the carbon nanofiber having the concave zinc oxide nanorod grown in Example 1 was 3.13 eV.

Comparative Example  One

The zinc oxide nanoparticles from Sigma Aldrich were used as photocatalysts in water degradation by sunlight.

Experimental Example: Photovoltaic  Through investigation Water decomposition  Measurement of hydrogen produced in the process

In order to measure the hydrogen production efficiency, the amount of hydrogen produced through the water decomposition process during the solar irradiation was measured using the zinc oxide of Example 1, Example 2, and Comparative Example 1.

The carbon nanofibers and zinc oxide particles on which the zinc oxide nano-rods prepared by the methods of Examples 1 and 2 and Comparative Example 1 were grown were subjected to Xe arc lamp (Newport, 300 W ), The efficiency of hydrogen production using water decomposition was measured. The measurement of the generated water was performed using a gas chromatograph (Agilent GC 6890N).

Specifically, the qualitative analysis of hydrogen produced by using the thermal conductivity detector which can measure the qualitative measurement of the gas using the inherent thermal conductivity difference value of the gas was performed. The size of the sample was fixed to 1 cm × 3 cm. By the sunlight, zinc oxide basically generates electrons and holes by the photoelectric effect. Electrons combine with protons present in water to form hydrogen. This hydrogen production reaction is in competition with the reaction of electron and hole recombination. In general, hydrogen production efficiency is measured by adding a sacrificial reagent which eliminates the holes generated to suppress the recombination reaction.

In this example, Na ₂ S and Na ₂ SO ₃ were fixed at a concentration of 0.1 M, respectively, as the sacrificial reagent used. FIGS. 6 and 7 show production characteristics of hydrogen using the water decomposition process by irradiation of sunlight using the carbon nanofibers grown by the above-described method, Respectively.

division Specific surface area
(cm < ² > / g) Band gap
(eV) Concentration (mM) of zinc acetate Electrochemical deposition conditions
(Voltage (V), time (minute)) Length of zinc oxide (nm) Hydrogen production rate
(μmol / h) Example 1 12.43 3.04 0.25 -1, 30 457 0.4257 Example 2 9.04 3.13 0.50 -1, 30 492 0.2261 Comparative Example 1 8.45 3.24 ZnO: 0.4 mg - 20 0.0167

As shown in Table 1, the hydrogen production rate of Example 1 was about two times higher than that of Example 2. This is due to the difference between the specific surface area of the sample and the band gap energy due to the difference in the shape of the zinc oxide nano-rods. The specific surface area of the sample was about 3 cm ² / g higher than that of Example 2, and the band gap energy of Example 1 was smaller than that of Example 2, .

The hydrogen generation rate in Example 1 was about 40 times higher than that in Comparative Example 1. It can be seen that this is due to the difference in the electrical conductivity and adsorption characteristics of the carbon nanofibers and the shape of the zinc oxide.

Claims (20)

a) preparing a mixed solution by adding a polyacronitrile (PAN) polymer to N, N-dimethylformamide (DMF) and stirring;
b) electrospinning the mixed solution to produce a polymer nanofiber;
c) firing the polymer nanofibers to produce carbon nanofibers; And
d) growing a zinc oxide nanorod having a concave end portion on the carbon nanofibers through electrochemical deposition;
The firing in the step c) is carried out by heating the electrospun nanofibers at a rate of 5 ° C / min, maintaining the temperature at 250 ° C for 20 minutes, increasing the temperature to 750 ° C at a rate of 5 ° C / min, maintaining the temperature at 750 ° C for 1 hour, To 5 占 폚 / min and then held at 1400 占 폚 for 1 hour,
(D) electrochemical deposition is performed by electrodeposition using 0.25 mM zinc acetate as a zinc oxide precursor, followed by drying at 400 DEG C for 30 minutes.
A method for producing a carbon nanofiber in which a zinc oxide nanorod having a concave end portion is grown. The method according to claim 1,
A method for producing a carbon nanofiber in which a zinc oxide nanorod having a concave end portion is grown is characterized in that the mixed solution of step a) contains 5 to 20 wt% of PAN based on the total weight. The method according to claim 1,
wherein a voltage of 5 to 100 kV is applied during the step of electrospinning the b) step. delete delete The method according to claim 1,
wherein the step (d) is carried out at 50 to 80 ° C. delete delete The method according to claim 1,
wherein the zinc oxide nanorod having a concave end portion is grown, wherein potassium chloride is used as an electrolyte in the electrochemical deposition process of step (d). In the ninth aspect,
Wherein the concentration of the potassium chloride is 0.1 mM to 0.5 mM, and the zinc oxide nanorod having a concave end portion is grown. The method according to claim 1,
and a step of applying a voltage of -20 V to a voltage of -1 V to perform electrochemical deposition in step d). The method according to claim 1,
wherein the step d) is carried out for 15 minutes to 5 hours. An electrode using the carbon nanofibers produced according to the method of claim 1, wherein the zinc oxide nanorod having a concave end portion is grown. 14. The method of claim 13,
Wherein the zinc oxide nanorod has a length of 100 nm to 1 m. 14. The method of claim 13,
Wherein the zinc oxide nanorod has a diameter ranging from 20 nm to 300 nm. 14. The method of claim 13,
Wherein the length of the carbon nanofibers is in the range of 100 nm to 10 mu m. 14. The method of claim 13,
Wherein the diameter of the carbon nanofibers ranges from 50 nm to 2 mu m. 14. The method of claim 13,
Wherein the aspect ratio of the carbon nanofibers is in the range of 2 to 100. < Desc / Clms Page number 13 > delete An electrochemical cell comprising an electrode, an electrolyte and a counter electrode according to claim 13.

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