An azo cross-linked nitrogen-doped graphene electrode material, a preparation method thereof and application thereof in supercapacitors

Abstract

The application discloses an azo-crosslinked nitrogen-doped graphene electrode material, a preparation method thereof and application of the electrode material in supercapacitors, and the nitrogen-doped graphene electrode material is a layered electrode material, and azobenzene groups are contained between graphene layers to form a pillared structure; the preparation method comprises the following steps: adding graphene oxide, sodium dodecyl sulfonate and 4-nitro diazonium benzene tetrafluoroborate into a solvent, and obtaining an intermediate product of nitro-functionalized graphene oxide after heating reaction; and then dispersing the intermediate product into a solvent, adding urea, and obtaining the nitrogen-doped graphene electrode material with the pillared structure after hydrothermal reaction. The nitrogen-doped graphene electrode material with the pillared structure has excellent electrochemical performance, and has a wide application prospect in the fields of energy and electronic devices.

Description

Technical Field

[0001] This invention relates to an electrode material, its preparation method, and its application in supercapacitors, and more particularly to an azo-crosslinked nitrogen-doped graphene electrode material, its preparation method, and its application in supercapacitors. Background Technology

[0002] The increasing consumption of traditional fossil fuels and the growing severity of environmental problems have driven the development of clean energy technologies, particularly efficient energy storage systems. Among these, supercapacitors have attracted widespread attention and research due to their advantages such as high power density, ultra-long cycle life, fast charge / discharge rates, and high safety, making them one of the most promising energy storage systems. However, carbon materials, conductive polymers, and metal oxides, as important electrode materials for supercapacitors, still have their limitations. For example, carbon-based electrode materials possess excellent conductivity and stability, but their storage capacity is low due to limitations in charge storage mechanisms; metal oxides have high specific capacitance but poor conductivity; and while conductive polymers have high theoretical specific capacitance, good conductivity, and processability, volume expansion / contraction during charge / discharge processes leads to poor cycle stability.

[0003] Graphene has become a highly efficient electrode material for electric double-layer capacitors due to its unique physicochemical properties. As a two-dimensional carbon material, graphene possesses a large surface area (2630 nm). 2 ·g -1 Graphene nanosheets possess excellent thermal conductivity and high chemical stability. However, their electrochemical energy storage performance is limited by their tendency to aggregate. Modification, doping, or the construction of composite materials are often used to improve their electrochemical performance. Therefore, there is an urgent need to develop a doped graphene electrode material with superior electrochemical performance. Summary of the Invention

[0004] Objective of the invention: This invention aims to provide an azo-crosslinked nitrogen-doped graphene electrode material with excellent electrochemical performance; this invention also aims to provide a method for preparing the azo-crosslinked nitrogen-doped graphene electrode material; this invention further aims to provide an application of the azo-crosslinked nitrogen-doped graphene electrode material in supercapacitors.

[0005] Technical solution: The azo crosslinked nitrogen-doped graphene electrode material of the present invention is a layered electrode material, in which azo phenyl groups are contained between the graphene sheets to form a pillar structure.

[0006] Further, the method includes: adding graphene oxide, sodium dodecyl sulfonate and 4-nitrodiazobenzene tetrafluoroborate to a solvent, heating and reacting to obtain an intermediate product, nitrofunctionalized graphene oxide; then dispersing the intermediate product in a solvent, adding urea, and hydrothermally reacting to obtain a nitrogen-doped graphene electrode material with a pillar structure.

[0007] Furthermore, the mass ratio of graphene oxide, sodium dodecyl sulfonate, and 4-nitrodiazobenzene tetrafluoroborate is 1:0.01:0.5-1, the heating reaction temperature is 45-60℃, the reaction time is 4-8h, the mass ratio of intermediate product to urea is 1:10-1:20, the hydrothermal reaction temperature is 140-180℃, and the reaction time is 16-20h.

[0008] Furthermore, the product after the hydrothermal reaction is subjected to solid-liquid separation, washing, and freeze-drying to obtain the target electrode material, wherein the solvent is water.

[0009] Furthermore, the intermediate product is uniformly dispersed in the solvent by ultrasonic dispersion for 0.5 to 3 hours.

[0010] The nitrogen-doped graphene electrode material can be used in supercapacitors.

[0011] Invention principle: The preparation method of the present invention utilizes a diazotization reaction to nitrofunctionalize the graphene oxide matrix. Under the premise of reducing graphene oxide, nitrogen doping is carried out using urea. At the same time, the alkaline environment generated by the high-temperature decomposition of urea promotes the azotization reaction of the nitro groups, thereby constructing an azophenyl compound with a rigid structure and conjugated system between the graphene sheets, thus avoiding the accumulation of graphene.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: The nitrogen-doped graphene electrode material has excellent electrochemical performance. This electrode material is constructed with two-dimensional graphene as the matrix to form a layered electrode material, which increases the specific surface area of ​​the material and improves the double-layer capacitance. At the same time, pseudocapacitance is introduced by introducing heteroatom nitrogen and utilizing the reversible redox properties of conjugated azo groups, which exerts a synergistic effect under the dual mechanism and improves its capacitance. Attached Figure Description

[0013] Figure 1 A schematic diagram illustrating the synthesis of nitrogen-doped graphene electrode materials with a pillared structure;

[0014] Figure 2 FTIR spectra of GO, NO2-GO, and AZO-NGE;

[0015] Figure 3 N1s XPS spectra of NGE, NO2-GO, and AZO-NGE;

[0016] Figure 4 For NGE and AZO-NGE at 6 mol·L -1 In KOH solution, the scan rate is 10 mV·s -1Cyclic voltammetry curves at current density of 0.1 A·g -1 Constant current charge-discharge curve at time;

[0017] Figure 5 AZO-NGE at 6 mol·L -1 Cyclic voltammetry curves at different scan rates and constant current charge-discharge tests at different current densities in KOH;

[0018] Figure 6 The specific capacitance of AZO-NGE at different current densities;

[0019] Figure 7 AZO-NGE at 6 mol·L -1 AC impedance curves in KOH. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0021] Example 1

[0022] 100 mg of graphene oxide (GO) was placed in 100 mL of deionized water, and 1 mg of sodium dodecyl sulfonate (SDS) was added for ultrasonic dispersion for 1 h. Then, 100 mg of 4-nitrodiazobenzene tetrafluoroborate was added to the solution and ultrasonically dispersed until homogeneous. The mixture was then transferred to a 250 mL flask and reacted at 45 °C for 8 h. After centrifugation and washing, the intermediate product, nitrofunctionalized graphene oxide (NO2-GO), was obtained. This intermediate product was then ultrasonically dispersed in 100 mL of deionized water for 1 h. Next, 20 g of urea was added to the homogeneous dispersion and ultrasonically dissolved for 30 min. The solution was then transferred to a hydrothermal reactor and reacted at 180 °C for 20 h. After solid-liquid separation, washing, and freeze-drying, a pillar-structured nitrogen-doped graphene (AZO-NGE) electrode material was obtained. (See the schematic diagram for the synthesis.) Figure 1 .

[0023] Example 2

[0024] 100 mg of graphene oxide (GO) was placed in 100 mL of deionized water, and 1 mg of sodium dodecyl sulfonate (SDS) was added for ultrasonic dispersion for 1 h. Then, 50 mg of 4-nitrodiazobenzene tetrafluoroborate was added to the above solution and ultrasonically dispersed evenly. Finally, it was transferred to a 250 mL flask and reacted at 60 °C for 4 h. After centrifugation and washing, the intermediate product nitrofunctionalized graphene oxide (NO2-GO) was obtained. It was then placed in 100 mL of deionized water and ultrasonically dispersed for 1 h. Then, 10 g of urea was added to the above evenly dispersed solution and ultrasonicated for 30 min to completely dissolve the urea. It was then transferred to a hydrothermal reactor and reacted at 140 °C for 18 h. After solid-liquid separation, washing, and freeze-drying, a pillar-structured nitrogen-doped graphene (AZO-NGE) electrode material was obtained.

[0025] Example 3

[0026] 100 mg of graphene oxide (GO) was placed in 100 mL of deionized water, and 1 mg of sodium dodecyl sulfonate (SDS) was added for ultrasonic dispersion for 1 h. Then, 80 mg of 4-nitrodiazobenzene tetrafluoroborate was added to the above solution and ultrasonically dispersed evenly. Finally, it was transferred to a 250 mL flask and reacted at 55 °C for 6 h. After centrifugation and washing, the intermediate product nitrofunctionalized graphene oxide (NO2-GO) was obtained. It was then placed in 100 mL of deionized water and ultrasonically dispersed for 1 h. Then, 15 g of urea was added to the above evenly dispersed solution and ultrasonicated for 30 min to completely dissolve the urea. It was then transferred to a hydrothermal reactor and reacted at 160 °C for 16 h. After solid-liquid separation, washing, and freeze-drying, a pillar-structured nitrogen-doped graphene (AZO-NGE) electrode material was obtained.

[0027] Comparative Example

[0028] 100 mg of GO was ultrasonically dispersed in 100 mL of deionized water for 1 hour. Then, 20 g of urea was added to the above uniformly dispersed solution and ultrasonicated for 30 minutes to completely dissolve the urea. The solution was then transferred to a hydrothermal reactor and reacted at 180 °C for 20 hours. After solid-liquid separation, washing, and freeze-drying, nitrogen-doped graphene (NGE) electrode material was obtained.

[0029] Depend on Figure 2 As shown, different oxygen-containing groups can be seen from the infrared spectrum of graphene oxide (GO), such as C=O (1735cm). -1 ), COC (1240cm) -1 ) and C-OH (1080cm) -1 An infrared absorption peak for NO2 (1523 cm⁻¹) was found in the infrared spectrum of NO₂-GO. -1This indicates that graphene oxide has been successfully functionalized with nitro groups. In the infrared spectrum of AZO-NGE prepared in Example 1, a comparison revealed that the characteristic infrared absorption peaks of the oxygen-containing groups were significantly weakened or disappeared, indicating that GO was effectively reduced through a high-temperature hydrothermal reaction with the addition of urea. Simultaneously, a new infrared absorption peak appeared at 1451 cm⁻¹. -1 The significantly weakened infrared absorption peak of NO2 (N=N) indicates that the nitro groups underwent an azotization reaction during the reduction of nitrated graphene oxide (NO2-GO). Therefore, the synthesis route of the AZO-NGE electrode material designed in this invention is feasible.

[0030] Depend on Figure 3 The N1s XPS spectrum of NGE shows three fitting peaks for nitrogen doping: Pyridinic N, Pyrrolic N, and Graphitic N, indicating that heteroatom nitrogen was successfully doped into the graphene structure. The N1s XPS spectrum of NO2-GO prepared in Example 1 shows that the present invention successfully achieved nitro grouping of GO. Furthermore, the N1s XPS spectrum of AZO-NGE not only shows fitting peaks for nitrogen doping but also reveals fitting peaks for N=N, indicating that the nitro groups underwent further azotization during the hydrothermal process. This further proves the feasibility of the synthesis route for the AZO-NGE electrode material designed in this invention.

[0031] Depend on Figure 4 The cyclic voltammetry (CV) curves show that the area of ​​the closed CV curve of AZO-NGE in Example 1 is significantly larger than that of the comparative NGE, indicating that the specific capacitance of the AZO-NGE electrode material is higher than that of NGE. Simultaneously, a clear redox peak appears on the CV curve of AZO-NGE, indicating that the AZO-NGE electrode material not only possesses double-layer capacitance but also exhibits pseudocapacitance from nitrogen doping and azotization. This suggests that this electrode material combines both double-layer capacitance and Faraday pseudocapacitance energy storage mechanisms, which will significantly improve its electrochemical performance. The constant current charge-discharge curves are used to evaluate the electrochemical performance of the electrode material under controlled current density. The charge-discharge curve of AZO-NGE resembles a symmetrical triangle, but also exhibits slight distortion, further demonstrating that the specific capacitance of the AZO-NGE electrode material originates from the combination of double-layer capacitance and pseudocapacitance. A comparison of the figures also shows a significant difference in discharge time between the two electrode materials. The AZO-NGE has a discharge time of up to 3900s, indicating that it has a high specific capacitance (437.8F / g), while the specific capacitance of the comparative NGE is only 283.9F / g.

[0032] At different scan rates (1mV·s) -1 ~100mV·s -1Cyclic voltammetry curves Figure 5 A rectangular shape accompanying the redox peaks is clearly visible, and the positions of the redox peaks shift with increasing scan rate, indicating the behavior of double-layer capacitance and good ion diffusion. The high current response indicates that this electrode material has high conductivity and low internal resistance. Furthermore, the current response gradually increases with increasing scan rate, and the shape of the cyclic voltammetry curve remains essentially unchanged, indicating that the AZO-NGE electrode material prepared in Example 1 exhibits good conductivity at 6 mol·L⁻¹. -1 KOH exhibits excellent rate capability and stability, possibly due to the combined and synergistic effect of two energy storage mechanisms, which improves the electrochemical performance of the composite material. As shown in the charge-discharge curves of the AZO-NGE electrode material at different current densities, with increasing current density, the discharge time gradually shortens, leading to a gradual decrease in specific capacitance. Figure 6 As shown.

[0033] AC impedance spectroscopy can effectively analyze the electrochemical performance of electrode materials. An ideal Nernst curve consists of a semicircular arc in the high-frequency region and a straight line in the low-frequency region. Figure 7 The results show that the AZO-NGE electrode material is used in 6 mol·L⁻¹ applications. -1 The AC impedance spectra in KOH show a small arc in the high-frequency region, while the slope of the straight line in the low-frequency region reflects the capacitive behavior of the electrode material. For AZO-NGE, the diameter of the semi-circular arc is approximately 0.5 Ω, indicating that this electrode material has a low transfer resistance. Conversely, the slope of the straight line for AZO-NGE is closer to 90°, indicating that this electrode material has good capacitive behavior, a result consistent with the cyclic voltammetry results mentioned above. These superior electrochemical properties likely stem from the ideal combination of the spatial structure designed in this invention, as well as the interaction and synergistic effect of the two energy storage mechanisms.

Claims

1. An azo-crosslinked nitrogen-doped graphene electrode material, characterized in that, It is a layered electrode material, with azophenyl groups forming a pillar structure between graphene sheets; The preparation method of the azo crosslinked nitrogen-doped graphene electrode material includes: adding graphene oxide, sodium dodecyl sulfonate and 4-nitrodiazobenzene tetrafluoroborate to a solvent, heating and reacting to obtain the intermediate product nitrofunctionalized graphene oxide; then dispersing the intermediate product in a solvent, adding urea, and hydrothermally reacting to obtain the pillared nitrogen-doped graphene electrode material.

2. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The mass ratio of graphene oxide, sodium dodecyl sulfonate, and 4-nitrodiazobenzene tetrafluoroborate is 1:0.01:0.5-1.

3. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The heating reaction temperature is 45-60℃, and the reaction time is 4-8h.

4. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The mass ratio of the intermediate product to urea is 1:10 to 1:

20.

5. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The hydrothermal reaction temperature is 140-180℃, and the reaction time is 16-20h.

6. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The product after hydrothermal reaction is subjected to solid-liquid separation, washing, and freeze-drying to obtain the target electrode material.

7. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The solvent is water.

8. The azo-crosslinked nitrogen-doped graphene electrode material according to claim 1, characterized in that, The intermediate product was uniformly dispersed in the solvent by ultrasonic dispersion for 0.5 to 3 hours.

9. The application of the azo-crosslinked nitrogen-doped graphene electrode material of claim 1 in a supercapacitor.

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