A method for preparing graphene-transition metal oxide composite electrode material by plasma

Abstract

The invention discloses a method for preparing a graphene-transition metal oxide composite electrode material by plasma, characterized in that the steps are included: Step 1: adding graphene oxide to anhydrous ethanol, and obtaining a uniformly dispersed graphene oxide suspension after ultrasonic mixing; adding an ethanol solution of a transition metal salt or adding compound A and compound B that can react chemically to produce a transition metal salt, stirring and mixing uniformly; placing the mixture in a centrifuge tube, separating it using a centrifuge, washing it by centrifugation with anhydrous ethanol, and drying the remaining suspension in a drying oven to obtain a powdered graphene-transition metal oxide precursor. The effective specific surface area of ​​the graphene-transition metal oxide composite electrode material prepared by the method of the present invention increases, and the capacitance performance of the graphene-transition metal oxide composite electrode material as the active electrode material of a supercapacitor is optimized.

Description

Technical Field

[0001] The invention relates to the technical field of electrode materials for supercapacitors, and in particular to a method for preparing a graphene-transition metal oxide composite electrode material by plasma. Background Art

[0002] The new energy industry is booming under the dual carbon goals. However, due to the intermittent output of solar energy, wind energy, etc. due to regional and seasonal changes, they will bring quality problems such as voltage and frequency fluctuations when connected to the power grid. Adding energy storage links to the power system can make the power system more "flexible" and improve the flexibility and safety of power grid operation. Therefore, energy storage technology has become a key link in the development of new energy. Supercapacitors, as a new type of green energy storage device, have the advantages of high specific capacitance, fast charging and discharging, and long cycle life. The selection and optimization of its electrode materials play a key role in improving performance. How to increase energy density and specific capacitance as much as possible without losing power density has become the main problem that electrode materials need to overcome.

[0003] At present, the more common electrode materials include carbon materials and transition metal oxides. Carbon materials have high specific surface area and high stability. In particular, graphene, as a two-dimensional (2D) single-layer carbon material, has excellent physical and chemical properties and is easy to modify. However, its charge storage capacity is weak and it is difficult to meet the performance requirements of special fields such as energy devices with higher energy storage properties. Transition metal oxides have pseudoelectricity and store energy through reversible chemical reactions. Compared with carbon materials, they have strong charge storage capacity, but most of them have poor conductivity, low power density, and poor cycle stability. With the expansion of the demand for supercapacitor applications, simple graphene materials or transition metal oxide electrodes are difficult to meet the needs, and new supercapacitor electrode materials with high energy and high power density and good cycle stability are urgently needed. In order to improve the performance of electrode materials, graphene-transition metal oxide composites are prepared to give full play to their respective advantages and have the characteristics of high specific energy density and high specific power density.

[0004] In order to prepare electrode materials with both high specific energy density and high specific power density, sol-gel method, electrodeposition method, chemical deposition method, hydrothermal method, etc. are usually used to prepare transition metal oxides and graphene materials, so that the composite electrode materials have synergistic effects and have achieved certain results. These preparation methods or processes are relatively complicated, or the precise control is difficult and costly, or the secondary pollution cannot meet the environmental protection issues. In recent years, due to its rich active electrons, ions, free radicals and certain physical bombardment effects, the potential of low-temperature plasma technology in material preparation has been gradually developed, and it has also shown many advantages in the preparation of graphene composite materials. Plasma material preparation technology can affect the structural size, chemical composition, and appearance of the material by changing the discharge operation parameters, thereby improving the material performance. It has the advantages of good universality, mild reaction conditions, and controllable preparation effect, and provides an effective way to prepare supercapacitor electrode materials and improve their performance.

[0005] Therefore, in order to prepare an electrode material having both high specific energy density and high specific power density, the present invention provides a method for preparing a graphene-transition metal oxide composite electrode material by plasma. Summary of the invention

[0006] 1. Technical problems to be solved:

[0007] In view of the above technical problems, the present invention provides a method for preparing graphene-transition metal oxide composite electrode materials by plasma.

[0008] 2. Technical solution:

[0009] A method for preparing a graphene-transition metal oxide composite electrode material by plasma, comprising the following steps:

[0010] Step 1: adding graphene oxide to anhydrous ethanol, and obtaining a uniformly dispersed graphene oxide suspension after ultrasonic mixing; adding an ethanol solution of a transition metal salt or adding compound A and compound B that can undergo a chemical reaction to produce a transition metal salt, and stirring and mixing evenly; placing the mixture in a centrifuge tube, separating it using a centrifuge, centrifugally washing it with anhydrous ethanol, and drying the remaining suspension in a drying oven to obtain a powdered graphene-transition metal oxide precursor;

[0011] Step 2: placing the graphene-transition metal oxide precursor into the plasma region of the dielectric barrier discharge reactor, using a nanosecond pulse power supply as an excitation source; and introducing a working gas into the dielectric barrier discharge reactor;

[0012] Step 3: Change the voltage amplitude, frequency, rising edge, falling edge and pulse width parameters of the nanosecond pulse power supply to generate plasma to treat the graphene-transition metal oxide precursor.

[0013] Furthermore, the transition metal salt is Ni(CH 3 COO 2 ·4H 2 O、Zn(CH 3 COO 2 ·2H 2 O、Mn(CH 3 COO 2 ·4H 2 One of O.

[0014] Furthermore, the compound A and compound B are nickel carbonate and acetic acid or zinc carbonate and acetic acid respectively.

[0015] Furthermore, the working gas is argon.

[0016] Furthermore, the mass volume ratio concentration of the graphene oxide suspension is 15g / L-20g / L; the molar concentration of the ethanol solution of the transition metal salt is 0.02mol / L-0.05mol / L; and the volume ratio of the graphene oxide suspension to the ethanol solution of the transition metal salt is 50-70:30-50.

[0017] Furthermore, the drying temperature of the drying oven is 70°C-120°C, preferably 80°C.

[0018] Furthermore, the voltage amplitude of the nanosecond pulse power supply is 3kV-8kV; the frequency is 1kHz-7kHz, the rising edge is 50ns-500ns, the falling edge is 50ns-500ns, and the pulse width parameter is 300ns-2000ns; the time for plasma to treat the graphene-transition metal oxide precursor is 10min-30min.

[0019] The working principle of the present invention for treating graphene-transition metal oxide precursors by plasma is as follows: when graphene oxide is placed in the plasma reaction area, the bombardment of high-energy particles with a certain energy causes the polar chemical bonds of some oxygen-containing functional groups (carboxyl, hydroxyl, carbonyl, phenolic and other oxygen-containing functional groups, etc.) in the graphene oxide sheet to be distorted and broken, thereby generating a large amount of CO 2 In addition, the plasma itself has a certain temperature, which can further promote the decomposition of some oxygen-containing functional groups such as hydroxyl and carbonyl in graphene oxide by directly heating graphene oxide to generate CO 2 and gas molecules such as CO.

[0020] The high-energy active particles in the plasma promote the oxidation reaction of transition metal ions to generate oxides, and the oxygen atoms stripped from the graphene can also react with metal ions to generate oxides. The composite of graphene and metal oxide electrode materials with high theoretical capacity can significantly enhance the conductivity of the oxide itself, increase the transmission rate of electrons on its surface, increase the contact area between the active material and the electrolyte, and enhance the structural stability of the material. The resulting composite material exhibits excellent electrochemical performance in electrochemical supercapacitors.

[0021] A method for preparing a composite electrode material with both high specific energy density and high specific power density using atmospheric pressure plasma, wherein a graphene / transition metal oxide composite electrode material is prepared by treating a self-prepared precursor with plasma, and the performance of the prepared material is controlled by changing the plasma operating parameters.

[0022] 3. Beneficial effects:

[0023] (1) The surface of the graphene-transition metal oxide composite electrode material prepared by the method of the present invention undergoes significant volume expansion. The C content in the material increases, and the O content decreases by 20-30%, indicating that after being treated by the method of the present invention, the oxygen element in the graphene oxide is stripped off, and the graphene oxide is reduced to obtain graphene.

[0024] (2) The effective specific surface area of ​​the graphene-transition metal oxide composite electrode material prepared by the method of the present invention is increased, thereby optimizing the capacitance performance of the graphene-transition metal oxide composite electrode material when used as an active electrode material of a supercapacitor.

[0025] (3) Compared with the traditional material preparation method, the plasma preparation of graphene-transition metal oxide composite electrode materials in the present invention does not require the use of toxic reagents, the process is simple to operate, and is environmentally friendly and efficient.

[0026] (4) By adjusting the volume ratio of the graphene oxide suspension and the ethanol solution of the transition metal salt, different loadings of graphene-transition metal oxide precursors can be obtained, and further, composite electrode materials with different electrochemical properties can be obtained.

[0027] (5) Use plasma to directly process the precursor. The plasma reaction area can produce a high-energy active particle environment, allowing the precursor to react quickly in this environment, reducing the energy required for the reaction itself, increasing the reaction rate and reducing energy consumption.

[0028] (6) By changing the parameters of the plasma excitation source and the type of working gas, different discharge modes can be achieved, achieving different processing effects on the material and achieving the goal of controllable preparation effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a SEM image of the graphene-transition metal oxide precursor in Example 1 of the present invention;

[0030] Figure 2 This is a SEM image of the graphene-transition metal oxide composite electrode material in Example 1 of the present invention;

[0031] Figure 3 XPS spectrum of the graphene-transition metal oxide precursor in Example 1 of the present invention;

[0032] Figure 4 The XPS spectrum of the graphene-transition metal oxide composite electrode material in Example 1 of the present invention is as follows: Figure 4 ;

[0033] Figure 5 is the cyclic voltammetry curve of the graphene-transition metal oxide precursor in Example 1 of the present invention;

[0034] Figure 6 This is the cyclic voltammetry curve of the graphene-transition metal oxide composite electrode material in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be described in detail below with reference to the accompanying drawings.

[0036] like Figures 1 to 6 As shown,

[0037] Example 1

[0038] A method for preparing a graphene-transition metal oxide composite electrode material by plasma, comprising the following steps:

[0039] Step 1: Add 100 mg of graphene oxide to 60 ml of anhydrous ethanol and mix by ultrasonic to obtain a uniformly dispersed graphene oxide suspension; add Ni(CH 3 COO 2 ·4H 2 O (0.8mmol) in anhydrous ethanol (40ml), stirring for 2h with a magnetic stirrer to mix evenly; placing the mixture in a centrifuge tube, separating it with a centrifuge, pouring out the supernatant and re-adding anhydrous ethanol to continue centrifugation, after centrifugation washing three times, placing the remaining suspension in a drying oven at 80°C to dry, to obtain a powdered graphene-transition metal oxide precursor;

[0040] Step 2: Place the graphene-transition metal oxide precursor into the plasma region of a dielectric barrier discharge reactor (DBD), and use a nanosecond pulse power supply as an excitation source; introduce high-purity argon gas into the dielectric barrier discharge reactor at a flow rate of 0.5L / min, and add quartz wool at both ends of the plasma region to slow down the blowing force of the gas on the powder material and prevent the powder from being blown out of the plasma region;

[0041] Step 3: Set the voltage amplitude of the nanosecond pulse power supply to 6 kV, the frequency to 5 kHz, the rising edge to 50 ns, the falling edge to 50 ns, and the pulse width to 1000 ns, generate plasma to treat the graphene-transition metal oxide precursor for 30 minutes; and obtain the graphene-transition metal oxide composite electrode material after treatment.

[0042] The SEM image of the graphene-transition metal oxide precursor prepared in step 1 is as follows: Figure 1 As shown, the XPS spectrum of graphene-transition metal oxide precursor is as follows Figure 3 As shown;

[0043] The SEM image of the graphene-transition metal oxide composite electrode material prepared in step 3 is as follows: Figure 2 As shown; the XPS spectrum of graphene-transition metal oxide composite electrode material is as follows Figure 4 As shown;

[0044] The element contents of C, O, and Ni in the graphene-transition metal oxide precursor before plasma treatment and the graphene-transition metal oxide composite electrode material after treatment are shown in Table 1:

[0045] Table 1 Changes in element content of materials before and after plasma treatment

[0046]

[0047] Experimental results: SEM images of graphene-transition metal oxide precursors ( Figure 1 ) and SEM images of graphene-transition metal oxide composite electrode materials ( Figure 2 ) were compared and it was found that after plasma treatment, obvious volume expansion occurred on the surface of the material.

[0048] Analysis of Table 1 shows that after plasma treatment, the C content in the material increased by 23.24% and the O content decreased by 25.42%. This indicates that after plasma treatment, the oxygen element in the graphene oxide was stripped off and the graphene oxide was reduced to obtain graphene.

[0049] Electrode material performance test: The graphene-transition metal oxide precursor obtained in step 1 and the graphene-transition metal oxide composite electrode material obtained in step 3 were tested using a three-electrode test system. The results are as follows: Figure 4 and Figure 5 As shown, Figure 4 is the cyclic voltammetry curve of graphene-transition metal oxide precursor; Figure 5 Cyclic voltammetry curves of graphene-transition metal oxide composites.

[0050] The cyclic voltammetry curves of graphene-transition metal oxide precursors ( Figure 4 ) and cyclic voltammetry curves of graphene-transition metal oxide composites ( Figure 5 ), it can be found that the cyclic voltammetry curve area of ​​the material treated with plasma is larger and closer to a rectangle, indicating that the effective specific surface area of ​​the material increases after plasma treatment, which optimizes the capacitance performance of the composite material as an active electrode material of a supercapacitor.

[0051] Example 2

[0052] Step 1: Add 100 mg of graphene oxide to 100 ml of anhydrous ethanol and mix by ultrasonic to obtain a uniformly dispersed graphene oxide suspension; stir the suspension with a magnetic stirrer and slowly add NiCO 3 (0.8mmol) and CH 3 COOH (1.6mmol), nickel carbonate and acetic acid react in the graphene oxide suspension to form nickel acetate. During the growth of nickel acetate, graphene oxide will be doped, which can effectively increase the loading capacity of metal nickel and the binding mode is relatively firm, and it is not easy to fall off in subsequent reactions; during the stirring process, it was found that no more bubbles emerged in the solution, indicating that the reaction of nickel carbonate and acetic acid was completed, and stirring was continued for 2h to mix them evenly; the mixture was placed in a centrifuge tube and separated by a centrifuge, the supernatant was poured out and anhydrous ethanol was added again to continue centrifugation, and after centrifugal washing three times, the remaining suspension was placed in a drying oven at 80°C for drying to obtain a powdered graphene-transition metal oxide precursor;

[0053] Step 2: Place the graphene-transition metal oxide precursor into the plasma region of a dielectric barrier discharge reactor (DBD), and use a nanosecond pulse power supply as an excitation source; introduce high-purity argon gas into the dielectric barrier discharge reactor at a flow rate of 0.5L / min, and add quartz wool at both ends of the plasma region to slow down the blowing force of the gas on the powder material and prevent the powder from being blown out of the plasma region;

[0054] Step 3: Set the voltage amplitude of the nanosecond pulse power supply to 6 kV, the frequency to 5 kHz, the rising edge to 50 ns, the falling edge to 50 ns, and the pulse width to 1000 ns, generate plasma to treat the graphene-transition metal oxide precursor for 30 minutes; and obtain the graphene-transition metal oxide composite electrode material after treatment.

[0055] Example 3

[0056] Step 1: Add 100 mg of graphene oxide to 60 ml of anhydrous ethanol and mix by ultrasonic to obtain a uniformly dispersed graphene oxide suspension; add Zn(CH 3 COO 2 ·2H 2 O (0.8mmol) in anhydrous ethanol (40ml), stirring for 2h with a magnetic stirrer to mix evenly; placing the mixture in a centrifuge tube, separating it with a centrifuge, pouring out the supernatant and re-adding anhydrous ethanol to continue centrifugation, after centrifugation washing three times, placing the remaining suspension in a drying oven at 80°C to dry, to obtain a powdered graphene-transition metal oxide precursor;

[0057] Step 2: Place the graphene-transition metal oxide precursor into the plasma region of a dielectric barrier discharge reactor (DBD), and use a nanosecond pulse power supply as an excitation source; introduce high-purity argon gas into the dielectric barrier discharge reactor at a flow rate of 0.5L / min, and add quartz wool at both ends of the plasma region to slow down the blowing force of the gas on the powder material and prevent the powder from being blown out of the plasma region;

[0058] Step three: Set the voltage amplitude of the nanosecond pulse power supply to 6 kV, the frequency to 5 kHz, the rising edge to 50 ns, the falling edge to 50 ns, and the pulse width to 1000 ns, generate plasma to treat the graphene-transition metal oxide precursor for 30 minutes; obtain the graphene-transition metal oxide composite electrode material after treatment.

[0059] Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A method for preparing a graphene-transition metal oxide composite electrode material by plasma, characterized in that: The following steps are involved: Step 1: adding graphene oxide to anhydrous ethanol, and obtaining a uniformly dispersed graphene oxide suspension after ultrasonic mixing; adding an ethanol solution of a transition metal salt or adding compound A and compound B that can undergo a chemical reaction to produce a transition metal salt, and stirring and mixing evenly; placing the mixture in a centrifuge tube, separating it using a centrifuge, centrifugally washing it with anhydrous ethanol, and drying the remaining suspension in a drying oven to obtain a powdered graphene-transition metal oxide precursor; Step 2: placing the graphene-transition metal oxide precursor into the plasma region of a dielectric barrier discharge reactor, using a nanosecond pulse power supply as an excitation source; and introducing argon gas into the dielectric barrier discharge reactor; Step three: changing the voltage amplitude, frequency, rising edge, falling edge and pulse width parameters of the nanosecond pulse power supply to generate plasma to treat the graphene-transition metal oxide precursor; the voltage amplitude of the nanosecond pulse power supply is 3kV-8kV; the frequency is 1kHz-7kHz, the rising edge is 50ns-500ns, the falling edge is 50ns-500ns, and the pulse width parameter is 300ns-2000ns; the time for plasma to treat the graphene-transition metal oxide precursor is 10min-30min.

2. The method for preparing a graphene-transition metal oxide composite electrode material by plasma according to claim 1, characterized in that: The transition metal salt is one of Ni(CH3COO)2·4H2O, Zn(CH3COO)2·2H2O, and Mn(CH3COO)2·4H2O.

3. The method for preparing a graphene-transition metal oxide composite electrode material by plasma according to claim 1, characterized in that: The compound A and compound B are nickel carbonate and acetic acid or zinc carbonate and acetic acid respectively.

4. The method for preparing a graphene-transition metal oxide composite electrode material by plasma according to claim 3, characterized in that: The mass volume ratio concentration of the graphene oxide suspension is 15g / L-20g / L; the molar concentration of the ethanol solution of the transition metal salt is 0.02mol / L-0.05mol / L; the volume ratio of the graphene oxide suspension to the ethanol solution of the transition metal salt is 50-70:30-50.

5. The method for preparing a graphene-transition metal oxide composite electrode material by plasma according to claim 3, characterized in that: The drying temperature of the drying oven is 70°C-120°C.

Images