TWI639555B - Preparation method of nitrogen-doped graphene - Google Patents

Abstract

A method for preparing nitrogen-doped graphene, comprising providing a plasma electrolysis device, wherein the plasma electrolysis device has a nitrogen-containing electrolyte, and one of the plasma electrolysis devices is a graphite electrode; and providing a cathode current to the graphite The electrode is subjected to a plasma electrolysis reaction to obtain a nitrogen-doped graphene. The above method can prepare nitrogen-doped graphene by adding a nitrogen-containing electrolyte to the electrolyte at a relatively low voltage, a normal pressure, a temperature, and a very short time by a plasma electrolysis process.

Description

Method for preparing nitrogen-doped graphene

The invention relates to a method for preparing graphene, in particular to a method for preparing nitrogen-doped graphene.

Graphene is the latest nanocarbon material discovered. Graphene has many excellent properties, such as linear spectrum, high electron mobility, unique optical properties, high ductility, toughness, and only a single atom thickness. Therefore, graphene is considered to be in the fields of optoelectronics, energy, and chemical materials. A nanomaterial that brings breakthrough development. Nitrogen doping can open the energy gap of graphene and change its electronic structure to adjust the conductivity type. Nitrogen-doped graphene not only improves the carrier density and conductivity, but also improves stability. In addition, the surface-doped nitrogen atoms increase the activity of graphene on the adsorption of metal ions to increase the reactivity of graphene in the capacitance.

However, a conventional method for preparing nitrogen-doped graphene is chemical vapor deposition, which is a thin film process, and therefore, this method is less capable of mass production in an industrial grade. Another method of preparing nitrogen-doped graphene is to thermally reduce graphene oxide in an ammonia source. However, this method uses graphene to form graphene oxide, which is cumbersome and has a high degree of damage to the carbon atom lattice. In addition, both of the above methods must be produced at high temperatures and are time consuming.

In view of this, it is an urgent need to provide a high-efficiency nitrogen-doped graphene preparation method.

The invention provides a method for preparing nitrogen-doped graphene, which is to generate an aqueous solution cathode plasma reaction in an electrolyte containing a nitrogen source, to strip the cathode graphite and dope nitrogen atoms to produce nitrogen-doped graphene. The invention has the advantages of low cost, easy preparation, high efficiency and environmental friendliness.

A method for preparing nitrogen-doped graphene according to an embodiment of the present invention comprises: providing a plasma electrolysis device comprising an acidic electrolyte containing a nitrogen source, an anode, and a cathode, wherein the nitrogen source comprises NaNO ₃ , NaNO ₂ a combination of HNO ₃ or more, wherein the cathode is a graphite electrode; and a cathode current is supplied to the graphite electrode, and a surface of the graphite electrode in contact with the electrolyte is subjected to a solution cathodic plasma reaction to obtain a nitrogen gas. Graphene is doped, wherein the plasma electrolysis device has an output voltage of less than 150 V and an output current of 0.1 A to 2 A.

The purpose, technical contents, features, and effects achieved by the present invention will become more apparent from the detailed description of the appended claims.

10‧‧‧ electrolyte

20‧‧‧Anode

30‧‧‧ cathode

40‧‧‧Stirring magnet

1 is a schematic view showing a method of preparing nitrogen-doped graphene according to an embodiment of the present invention.

2a, 2b, and 2c are graphs showing the X-ray photoelectron spectroscopy of nitrogen-doped graphene produced by the preparation method of one embodiment of the present invention.

Attachment 1 is a scanning electron micrograph of a graphite electrode before being peeled off.

Annex 2 is a scanning electron micrograph of nitrogen-doped graphene produced by the preparation method according to an embodiment of the present invention.

Annex 3 is a transmission electron micrograph of nitrogen-doped graphene produced by the preparation method of one embodiment of the present invention.

Annex 4 is a high-magnification transmission electron micrograph of nitrogen-doped graphene produced by the preparation method according to an embodiment of the present invention.

Annex 5 to Annex 8 are the element distribution diagrams for energy scattering spectrometer analysis under a transmission electron microscope.

The embodiments of the present invention will be described in detail below with reference to the drawings. In addition to the detailed description, the present invention may be widely practiced in other embodiments, and any alternatives, modifications, and equivalent variations of the described embodiments are included in the scope of the present invention. quasi. In the description of the specification, numerous specific details are set forth in the description of the invention. In addition, well-known steps or elements are not described in detail to avoid unnecessarily limiting the invention. The same or similar elements in the drawings will be denoted by the same or similar symbols. It is to be noted that the drawings are for illustrative purposes only and do not represent the actual dimensions or quantities of the components. Some of the details may not be fully drawn in order to facilitate the simplicity of the drawings.

Please refer to FIG. 1 to illustrate a method for preparing nitrogen-doped graphene according to an embodiment of the present invention. First, a plasma electrolysis apparatus is provided which comprises an electrolyte 10 containing a nitrogen source, an anode 20 and a cathode 30, wherein the cathode 30 is a graphite electrode. The material of the anode 20 is not particularly limited and may be a metal electrode of a conductive material. For example, the material of the anode 20 may be stainless steel, titanium or platinum. Cathode 30 stone The ink electrode does not need to be purified in advance, so the material of the graphite electrode may be natural graphite, compressed graphite, partially graphite oxide or recycled graphite. It can be understood that in order to obtain nitrogen-doped graphene of better quality, the material of the graphite electrode can be high-purity graphite. The shape of the graphite electrode may be a cylindrical electrode or a sheet electrode.

Next, a cathode current is supplied to the graphite electrode of the cathode 30, and a surface of the graphite electrode in contact with the electrolyte 10 is subjected to a solution cathodic plasma reaction to obtain a nitrogen-doped graphene. The solution cathodic plasma reaction occurs at or near the surface of the graphite electrode of the cathode 30. In one embodiment, the wetted area of the anode 20 in the electrolyte 10 is greater than the wetted area of the graphite electrode of the cathode 30 in the electrolyte 10. Preferably, the wetted area of the anode 20 in the electrolyte 10 is much larger than the graphite electrode of the cathode 30. The wetted area of the electrolyte 10. For example, the wetted area of the anode 20 in the electrolyte 10 is greater than 10 times the wetted area of the graphite electrode of the cathode 30 in the electrolyte 10.

For ease of operation and safety considerations, in one embodiment, under the condition of appropriate electrolyte concentration, the output voltage of the plasma electrolysis device is less than 150V, and the cathode plasma can be produced. Preferably, the output voltage of the plasma electrolyzer is between 40V and 100V. The output current of the plasma electrolyzer is between 0.1A and 2A. It will be appreciated that the graphite electrode of the cathode 30 will be gradually consumed during the solution cathodic plasma reaction. Therefore, when the solution type cathode plasma reaction is performed, the graphite electrode of the cathode 30 can be moved to be immersed in the electrolyte 10 to maintain a stable output current.

The electrolyte 10 needs to achieve two functions, one of which is to cause a solution type cathodic plasma reaction, and the other is to provide a nitrogen source. In one embodiment, the electrolyte that causes the solution cathodic plasma reaction comprises an electrolyte that provides an alkali metal ion or provides a hydrogen ion. For example, the electrolyte providing the alkali metal ion may be LiOH, NaOH, KOH, Na ₂ SO ₄ , K ₂ NO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ or a combination thereof; the electrolyte providing the hydrogen ion may be sulfuric acid Or phosphoric acid. The electrolyte providing the nitrogen source may be NaNO ₃ , NaNO ₂ , HNO ₃ or a combination thereof, or NH ₄ NO ₃ , NH ₄ OH, NH ₄ Cl, (NH ₄ ) ₂ SO ₄ or a combination thereof. It should be noted that the electrolyte providing the nitrogen source can also be used as the electrolyte for causing the solution type cathode plasma reaction. For example, NaNO ₃ , NaNO ₂ and HNO ₃ have both functions.

It can be understood that different voltages are required to generate a cathodic plasma reaction depending on the conductivity, dissociation degree and concentration of different electrolytes. The concentration of the electrolyte can be such that the cathode plasma can be produced under the set voltage conditions. In general, the higher the concentration of the electrolyte, the lower the voltage required to produce a cathodic plasma reaction. For example, if the output voltage of the plasma electrolyzer is set to 60V, 2M LiOH electrolyte can be selected to add 2M NH ₄ OH. If the output voltage of the plasma electrolyzer is set to 70V, the concentration of the LiOH electrolyte can be reduced to 1.7M, and the concentration of NH ₄ OH is related to the amount of doping.

In one embodiment, the method for preparing nitrogen-doped graphene of the present invention further comprises heating the electrolyte 10 to 60 degrees Celsius to 80 degrees Celsius to facilitate the cathode plasma reaction. For example, the initial temperature of the electrolyte 10 can be 70 degrees Celsius. When the cathodic plasma reaction is carried out, the temperature of the electrolyte 10 is maintained at 70 to 80 degrees Celsius.

It can be understood that in order to improve the peeling of the graphite and the uniformity of the reaction, the electrolytic solution 10 can be stirred while performing the solution type cathode plasma reaction. For example, the stirring magnet 40 can be driven in the electrolyte 10 using a magnetic stirrer to agitate the electrolyte 10. Finally, nitrogen-doped graphene is separated from the electrolyte 10. For example, the method of separating nitrogen-doped graphene may be filtration or centrifugation, but is not limited thereto.

Preparation of nitrogen-doped graphene

The electrolyte is a strong acid or a strong base which can produce a solution-type cathodic plasma reaction, and then an electrolyte containing a nitrogen source. The cathode is a cut high-purity graphite sheet and is connected to a voltage supply (negative voltage output) having a width and a thickness of 1 cm and 0.013 cm, respectively, and a depth of 1 cm under the liquid surface of the electrolyte. The anode is a platinum sheet having a width and a thickness of 2 cm and 0.01 cm, respectively, and a depth of 10 cm under the liquid surface of the electrolyte. The cathode and the anode are connected to a DC power source and a bias voltage, and the voltage is gradually increased to produce a solution plasma on the surface of the cathode where the graphite sheet contacts the electrolyte. In this program, The temperature of the electrolyte is maintained at about 70 to 80 degrees Celsius. In order to improve the peeling efficiency and reduce the concentration gradient, a magnetic stirrer was used for stirring in the electrolyte and maintained at a speed of 200 rpm.

When a sufficiently high voltage is applied between the cathode and the anode, since the surface temperature of the cathode in contact with the electrolyte is too high (greater than the boiling point of water), a stable water vapor coating is formed on the surface of the cathode, and the graphite sheet starts to peel off. The nitrogen source in the electrolyte is also immediately doped into the stripped graphene. It should be noted that the tip position of the cathode can be lowered to maintain a current range of about 0.1 to 2A. The graphite sheet, which is immersed in the surface of the electrolyte at a depth of 1 cm, will be peeled off in as little as 10 to 30 seconds. After cooling to room temperature, the solution was passed through a PVDF film (average pore diameter of about 0.2 μm) supported by a porous glass frame by vacuum filtration to collect expanded graphene sheets. The prepared product was washed with deionized water and dried under vacuum at 60 ° C for 24 hours and then peeled off from the PVDF film.

Qualitative analysis

Annex 1 and Annex 2 are shown at the same magnification (x12000), and the appearance of the collected product before and after stripping of the graphite sheet by the solution type cathodic plasma reaction is observed by a scanning electron microscope. It can be seen from Annex 1 that the graphite flakes are a closely packed stack of carbon atom layers. Annex 2 shows that after peeling, the product is stacked in a sheet shape, like a deciduous shape.

Annex 3 and Annex 4 show transmission electron microscopy (TEM) photographs of nitrogen-doped graphene prepared under the above conditions. It can be seen from Annex 3 that the edges of the product and the surface are all characterized by graphene flakes. Annex 4 shows the photo of the edge of the graphene sheet observed at high magnification.

Annexes 5 to 8 are analysis of the energy dispersive spectroscopy (EDS) element distribution maps under a transmission electron microscope (TEM). Annex 5 is a dark field TEM image, and the white thin portion is the graphene produced by the above preparation conditions. Annex 6, Annex 7 and Annex 8 are the distribution of C, O and N elements on this graphene, respectively. From Annex 8, it can be confirmed that there is nitrogen doping on the graphene.

2a, 2b, and 2c are X-ray photoelectron spectroscopy of nitrogen-doped graphene produced by the above preparation conditions to further confirm the surface functional group bonding of the produced nitrogen-doped graphene. among them Figure 2a shows the full-spectrum scan. The signals of C, N and O are clearly observed in Figure 2a, indicating that the graphite sheet before the reaction has undergone oxidation and nitrogen doping after nitrogen doping. Then the above elements are scanned in detail. In the C1s map shown in Fig. 2a, the measured peaks can be separated into C=C, CC, CO/C=N and CN/CO bonds, as shown in Fig. 2b. Show. In the N1s map shown in Fig. 2a, in addition to the proof of nitrogen bonding, the peaks are divided into three different carbon-nitrogen bonding patterns of Pyridinic-N, Pyroric-N and Graphicic-N, as shown in Fig. 2c. Show.

In summary, the method for preparing nitrogen-doped graphene of the present invention can produce a cathode cathodic plasma reaction in an electrolyte containing a nitrogen source, and can make the cathode at a relatively low temperature, a general pressure, and a very short time. The graphite electrode is stripped and immediately doped with nitrogen to produce nitrogen-doped graphene. Therefore, the preparation method of the invention has the advantages of low cost, easy preparation, high efficiency and environmental friendliness.

The embodiments described above are only intended to illustrate the technical idea and the features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the contents of the present invention and to implement the present invention. That is, the equivalent variations or modifications made by the spirit of the present invention should still be included in the scope of the present invention.

Claims (15)

A method for preparing nitrogen-doped graphene, comprising: providing a plasma electrolysis device comprising an acidic electrolyte containing a nitrogen source, an anode, and a cathode, wherein the nitrogen source comprises NaNO ₃ , NaNO ₂ , HNO ₃ or a combination of the above, wherein the cathode is a graphite electrode; and providing a cathode current to the graphite electrode, performing a solution cathodic plasma reaction on the surface of the graphite electrode in contact with the acidic electrolyte to obtain a nitrogen-doped graphite The olefin, wherein the plasma electrolysis device has an output voltage of less than 150V and an output current of between 0.1A and 2A. The method for producing nitrogen-doped graphene according to claim 1, wherein the acidic electrolyte contains an electrolyte that provides an alkali metal ion or provides a hydrogen ion. The method for producing nitrogen-doped graphene according to claim 1, wherein the acidic electrolyte comprises Na ₂ SO ₄ , K ₂ NO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ or a combination thereof. The method for producing nitrogen-doped graphene according to claim 1, wherein the acidic electrolyte contains sulfuric acid or phosphoric acid. The method for preparing nitrogen-doped graphene according to claim 1, wherein a wetted area of the anode in the acidic electrolyte is larger than an infiltrated area of the graphite electrode in the acidic electrolyte. The method for preparing nitrogen-doped graphene according to claim 1, wherein the anode has a wetted area of the acidic electrolyte greater than 10 times the wetted area of the graphite electrolyte. The method for preparing nitrogen-doped graphene according to claim 1, wherein the output voltage of the plasma electrolysis device is between 40V and 100V. The method for preparing nitrogen-doped graphene according to claim 1, wherein the material of the graphite electrode comprises natural graphite, compressed graphite, partially graphite oxide or recycled graphite. The method for preparing nitrogen-doped graphene according to claim 1, wherein the material of the anode is stainless steel, titanium or platinum. The method for preparing nitrogen-doped graphene according to claim 1, wherein the solution-type cathode plasma reaction occurs on or near the surface of the graphite electrode. The method for preparing nitrogen-doped graphene according to claim 1, wherein when the solution-type cathode plasma reaction is performed, the graphite electrode is moved to be immersed in the acidic electrolyte. The method for preparing nitrogen-doped graphene according to claim 1, further comprising: heating the acidic electrolyte to 60 to 80 degrees Celsius. The method for preparing nitrogen-doped graphene according to claim 1, wherein the temperature of the acidic electrolyte is maintained at 70 to 80 degrees Celsius when the solution-type cathode plasma reaction is performed. The method for producing nitrogen-doped graphene according to claim 1, wherein the acidic electrolyte is stirred while the solution-type cathode plasma reaction is performed. The method for preparing nitrogen-doped graphene according to claim 1, further comprising: separating the nitrogen-doped graphene from the acidic electrolyte.