A method for vertical graphene surface modification for flexible supercapacitor electrodes

Abstract

The application discloses a vertical graphene surface modification method for a flexible supercapacitor electrode, and comprises the following steps: taking a carbon material as a substrate, growing vertical graphene on the substrate through a plasma-enhanced chemical vapor deposition method; placing the vertical graphene into a concentrated acid mixed solution; then, oxidizing the vertical graphene through an electrochemical oxidation method; and then, cleaning the oxidized vertical graphene to be neutral, and obtaining modified vertical graphene after drying treatment. The modified vertical graphene has a higher area specific capacitance, which can reach 1300 mF / cm 2 , which is 3 orders of magnitude higher than that of unmodified vertical graphene, and when the current density is increased from 1 mA / cm 2 to 20 mA / cm 2 , the capacitance retention rate is above 70%, and the modified vertical graphene has excellent rate performance. When the modified vertical graphene is assembled into a symmetric aqueous supercapacitor, the potential window can be expanded to 2 V; and the modification method provided by the application has the advantages of simple process, low cost, high performance and easy industrialization.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrode material preparation, and is suitable for energy catalysis application, in particular to a vertical graphene surface modification method for flexible supercapacitor electrode. BACKGROUND

[0002] Flexible supercapacitor is one of the most potential energy storage devices, which is mainly due to its high power density, excellent stability and light weight and easy to handle. However, many carbon materials such as graphene, carbon nanotubes and activated carbon have been widely prepared as electrode materials for supercapacitors. However, the flexible supercapacitors prepared by these electrode materials basically show poor specific rate performance. This is mainly due to the diffusion rate of ions in the electrolyte, the internal resistance of the electrode material and the large interfacial resistance between the electrochemically active material and the conductive substrate. Therefore, their specific capacitance shows low specific capacitance, such as graphene (100-210 F / g), single-walled carbon nanotubes (100-200 F / g), carbon fibers (1-2 F / g) and vertical graphene (100 μF / g), etc., so that carbon materials are rarely used directly as electrode materials. Vertical graphene has vertical orientation, so it shows large specific surface area, which is beneficial to the full contact of electrolyte, but due to its superhydrophobic property, it shows low specific capacitance in aqueous electrolyte, which limits its application in aqueous supercapacitors. Therefore, appropriate methods must be taken to modify the surface of vertical graphene to improve its surface activity and surface hydrophilicity, so that vertical graphene can be directly used as flexible electrode material and show considerable electrochemical performance.

[0003] At present, the commonly used surface treatment methods include KOH treatment, sulfuric acid treatment, nitric acid treatment, mixed acid treatment of nitric acid and sulfuric acid, plasma treatment and high temperature calcination treatment, etc. These methods often have the problems of complicated treatment, high cost, long time consumption, poor oxidation effect and reduced comprehensive performance of the material. Therefore, it is urgent to develop a vertical graphene surface modification method for flexible supercapacitor electrode with excellent performance. SUMMARY

[0004] The present application aims to at least solve one of the problems in the prior art, and provides a vertical graphene surface modification method for flexible supercapacitor electrode.

[0005] The technical solution of the present application is as follows:

[0006] The present application provides

[0007] A vertical graphene surface modification method for flexible supercapacitor electrode, comprising the following steps:

[0008] S1: growing vertical graphene on a carbon material as a substrate by plasma enhanced chemical vapor deposition method;

[0009] S2: placing the vertical graphene into a concentrated acid mixed solution;

[0010] S3: then oxidizing the vertical graphene by electrochemical oxidation method;

[0011] S4: finally washing the oxidized vertical graphene to neutral and performing drying treatment to obtain modified vertical graphene.

[0012] As a preferred scheme of the present application, in step S1, the carbon material comprises at least one of carbon cloth, carbon paper, carbon fiber, carbon nanotube and carbon tube.

[0013] As a preferred scheme of the present application, in step S1, the plasma generating device in the plasma enhanced chemical vapor deposition method comprises microwave plasma or radio frequency plasma emission device.

[0014] As a preferred scheme of the present application, in step S2, the concentrated acid mixed solution comprises concentrated nitric acid and concentrated sulfuric acid, and the volume ratio is 1:0-10.

[0015] As a preferred scheme of the present application, in step S3, the electrochemical oxidation method is a constant voltage method, and the voltage range is 0.1-20V.

[0016] As a preferred scheme of the present application, in step S3, the oxidation time of the constant voltage method is 0-120min.

[0017] As a preferred scheme of the present application, in step S4, the drying temperature is 40-80℃, and the drying time is 6-24h.

[0018] The present application has the following beneficial effects:

[0019] The present application provides a vertical graphene surface modification method for flexible supercapacitor electrode, vertical graphene is grown on carbon cloth by plasma enhanced chemical vapor deposition method, then the vertical graphene grown on the carbon cloth is placed in a mixed acid composed of concentrated nitric acid and concentrated sulfuric acid, then the vertical graphene surface is fully oxidized by short time constant voltage electrochemical oxidation to form many oxygen-containing functional groups. The electrochemical oxidation not only can make the top end of the vertical graphene be oxidized, but also can make the low end be fully oxidized, so that the vertical graphene with superhydrophobicity is changed into superhydrophilicity, which significantly improves the electrochemical performance of the vertical graphene, and the surface morphology and mechanical properties of the vertical graphene are not changed.

[0020] The modified vertical graphene surface prepared by the vertical graphene surface modification method has uniform surface, super-hydrophilic property, and excellent electrochemical performance, and when the current density is 1 mA / cm 2 , the specific capacitance value is 1500 mF / cm 2 , and when the current density is increased to 20 mA / cm 2 , the specific capacitance can still be maintained at 1000 mF / cm 2 , the capacitance retention rate is more than 70%, and the rate performance is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 SEM images of the unmodified vertical graphene prepared in Example 1 (b) and carbon cloth SEM images (a);

[0022] Figure 2 SEM images of the modified vertical graphene prepared in Example 1;

[0023] Figure 3 Contact angle images of the unmodified (a) and modified (b) vertical graphene prepared in Example 1;

[0024] Figure 4 Cyclic voltammetry characteristic curve of the modified vertical graphene prepared in Example 1. DETAILED DESCRIPTION

[0025] A vertical graphene modification method for a flexible supercapacitor electrode, comprising the following steps:

[0026] S1: growing vertical graphene on a substrate by plasma enhanced chemical vapor deposition method, wherein the substrate is at least one of carbon cloth, carbon paper, carbon sheet, carbon fiber and carbon nanotube, and preferably carbon cloth.

[0027] The plasma enhanced chemical vapor deposition method uses a microwave or radio frequency plasma emission device. Preferably, a radio frequency plasma emission device is used.

[0028] The gas used in the plasma enhanced chemical vapor deposition method for growing vertical graphene is hydrogen, argon and acetylene, and the volume ratio is 1:0-5:0-5, and preferably 10:10:15.

[0029] S2: placing the vertical graphene into a concentrated acid mixed solution, wherein the concentrated acid mixed solution is a mixed acid of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of the concentrated sulfuric acid and the concentrated nitric acid is 1:0-10, and preferably 1:2.

[0030] S3: Then the vertical graphene is oxidized by electrochemical oxidation method; the electrochemical method is constant voltage oxidation method; the electrochemical oxidation temperature is 20-50℃, and the time is 1-2h; preferably, the electrochemical oxidation temperature is 25℃, and the time is 10min.

[0031] The electrochemical method for oxidizing the vertical graphene includes constant voltage, constant current and pulse method.

[0032] S4: Finally, the oxidized vertical graphene is repeatedly washed to neutral and dried to obtain modified vertical graphene. The drying temperature is 50-100℃, and the time is 3-24h. Preferably, the drying temperature is 60℃, and the time is 12h.

[0033] The following is a preferred embodiment of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements are also considered within the scope of protection of the present application.

[0034] Example 1

[0035] The present application provides a vertical graphene surface modification method for flexible supercapacitor electrodes, comprising the following steps:

[0036] S1: First, cut a 5x5cm 2 carbon cloth, then clean it with ethanol and deionized water, and dry it at 60℃. Then put the cleaned carbon cloth into the equipment of plasma enhanced chemical vapor deposition, pass in hydrogen and argon with a volume ratio of 1:3, and a gas flow rate of 10sccm, then heat to 900℃ at a heating rate of 10℃ / min, then pass in acetylene with a gas flow rate of 20sccm, then turn on the plasma equipment with a power of 400W, and react for 1h. After the reaction, vertical graphene is grown on the carbon cloth (VG@CC), as shown in Figure 1 Fig. 1, where (a) is the SEM image of the carbon cloth, and (b) is the SEM image of the graphene grown on the carbon cloth. That is, the graphene is vertically grown on the carbon cloth.

[0037] S2: Measure 50mL of concentrated sulfuric acid (concentration ~98%) and 50mL of concentrated nitric acid (concentration ~65%) to prepare a mixed acid, then use an electrochemical workstation at a potential of 3V (vs. SCE) to perform electrochemical oxidation, using VG@CC as the working electrode, platinum wire as the counter electrode, SCE as the reference electrode, and the mixed acid as the electrolyte. The oxidation temperature is 25℃, and the oxidation time is 20min. After the reaction, wash with deionized water until neutral, and finally dry at 60℃ for 12h to obtain the surface modified VG@CC.

[0038] Figure 2 This is a scanning electron microscope (SEM) image of the modified vertical graphene prepared in this embodiment. As can be seen from the image, the modified vertical graphene... Figure 1 In comparison, its appearance remained basically unchanged.

[0039] Figure 3 The contact angle diagram of the modified vertical graphene prepared in this embodiment shows that after modification, the vertical graphene changes from superhydrophobic (a) to superhydrophilic (b), indicating that the surface of the modified vertical graphene has many hydrophilic groups.

[0040] Figure 4 The figure shows the cyclic voltammetric characteristics of the modified vertical graphene prepared in this embodiment. As can be seen from the figure, the cyclic voltammetric curves of the capacitor at different scan rates all have good symmetry and are close to rectangles, indicating that the modified vertical graphene has good capacitance characteristics.

[0041] To further verify the effect of electrochemical oxidation time on the specific capacitance of modified vertical graphene, with Example 1 as a reference, and keeping other experimental parameters and conditions unchanged, a first set of comparative experiments was set up by adjusting the electrochemical oxidation time, as shown in Table 1.

[0042] Table 1. Effect of different electrochemical oxidation times on the specific capacitance of modified vertical graphene.

[0043] Number Electrochemical oxidation time (min) Specific capacitance (mF / cm 2 )@ (1 mA / cm 2 ) 1 0 0.1 2 1 71.6 3 3 621.6 4 5 1103.3 5 7 1605.6 6 10 1497.8 7 20 1892.0

[0044] As can be seen from Table 1, the specific capacitance of the prepared modified vertical graphene increases with the extension of electrochemical oxidation time. Therefore, the preferred electrochemical oxidation time is 5 to 20 min.

[0045] Example 2

[0046] This invention provides a method for vertical graphene surface modification for flexible supercapacitor electrodes, comprising the following steps:

[0047] S1: First cut out a 5×5cm piece. 2 The carbon paper was then washed with ethanol and deionized water and dried at 60°C. Next, the washed carbon cloth was placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, and hydrogen and argon (volume ratio 1:5) were introduced at a flow rate of 7 sccm. The mixture was then heated to 900°C at a heating rate of 10°C / min, followed by the introduction of acetylene at a flow rate of 20 sccm. The plasma apparatus was then turned on at a power of 350W, and the reaction was allowed to proceed for 30 min. After the reaction, vertically grown graphene (VG@CP) was obtained on the carbon cloth.

[0048] S2: 50 mL of concentrated sulfuric acid (concentration of ~98%) and 50 mL of concentrated nitric acid (concentration of ~65%) are measured to prepare a mixed acid, and then electrochemical oxidation is carried out at a potential of 3V (vs. SCE) using an electrochemical workstation, with VG@CC as the working electrode, a platinum wire as the counter electrode, SCE as the reference electrode, and the mixed acid as the electrolyte, the oxidation temperature is 25℃, and the oxidation time is 20 min. After the reaction is completed, neutralize with deionized water, and finally dry at 60℃ for 12h to obtain the surface modified VG@CP.

[0049] When the modified vertical graphene prepared in Example 2 is subjected to electrochemical performance test, when the current density is 1mA / cm 2 , the specific capacitance is 1900mF / cm 2 , showing super high capacitive performance.

[0050] Example 3

[0051] The present application provides a vertical graphene surface modification method for flexible supercapacitor electrode, comprising the following steps:

[0052] S1: First, cut a piece of 5×5cm 2 carbon nanotube, then clean with ethanol and deionized water, and dry at 60℃. Then put the cleaned carbon cloth into the equipment of plasma enhanced chemical vapor deposition, pass in hydrogen and argon (volume ratio of 1:1), the gas flow rate is 6sccm, then heat to 900℃ at a rate of 10℃ / min, then pass in acetylene with a gas flow rate of 15sccm, then turn on the plasma equipment, the power is 300W, react for 45min. After the reaction, vertical graphene is grown on the carbon cloth (VG@CNT);

[0053] S2: 100 mL of concentrated sulfuric acid (concentration of ~98%) and 50 mL of concentrated nitric acid (concentration of ~65%) are measured to prepare a mixed acid, and then electrochemical oxidation is carried out at a potential of 3V (vs. SCE) using an electrochemical workstation, with VG@CC as the working electrode, a platinum wire as the counter electrode, SCE as the reference electrode, and the mixed acid as the electrolyte, the oxidation temperature is 25℃, and the oxidation time is 15 min. After the reaction is completed, neutralize with deionized water, and finally dry at 60℃ for 12h to obtain the surface modified VG@CNT.

[0054] When the modified vertical graphene prepared in Example 3 is subjected to electrochemical performance test, when the current density is 1mA / cm 2 , the specific capacitance is 1860mF / cm 2 , showing super high capacitive performance.

[0055] Example 4

[0056] This invention provides a method for vertical graphene surface modification for flexible supercapacitor electrodes, comprising the following steps:

[0057] S1: First cut out a 5×5cm piece. 2 The carbon cloth was then cleaned with ethanol and deionized water and dried at 60°C. Next, the cleaned carbon cloth was placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, and hydrogen and argon (volume ratio 1:10) were introduced at a flow rate of 8 sccm. The mixture was then heated to 850°C at a heating rate of 10°C / min, followed by the introduction of acetylene at a flow rate of 16 sccm. The plasma apparatus was then turned on at a power of 350W, and the reaction was allowed to proceed for 40 min. After the reaction, vertically grown graphene (VG@C) was obtained on the carbon cloth.

[0058] S2: Prepare a mixed acid by measuring 100 mL of concentrated sulfuric acid (concentration ~98%) and 40 mL of concentrated nitric acid (concentration ~65%). Then, use an electrochemical workstation at a potential of 3V (vs. SCE), with VG@CC as the working electrode, platinum wire as the counter electrode, SCE as the reference electrode, and the mixed acid as the electrolyte for electrochemical oxidation. The oxidation temperature is 25℃, and the oxidation time is 16 min. After the reaction, wash with deionized water until neutral, and finally dry at 60℃ for 12 h to obtain surface-modified VG@C.

[0059] When the modified vertical graphene prepared in Example 4 was subjected to electrochemical performance testing, the current density was 1 mA / cm². 2 At that time, the specific capacitance was 1728 mF / cm. 2 It exhibits extremely high capacitance performance.

[0060] Example 5

[0061] This invention provides a method for vertical graphene surface modification for flexible supercapacitor electrodes, comprising the following steps:

[0062] S1: First cut out a 5×5cm piece. 2 The carbon fiber was then washed with ethanol and deionized water and dried at 60°C. Next, the washed carbon cloth was placed in a plasma-enhanced chemical vapor deposition (PECVD) apparatus, and hydrogen and argon (volume ratio 1:5) were introduced at a flow rate of 7 sccm. The mixture was then heated to 950°C at a heating rate of 10°C / min, followed by the introduction of acetylene at a flow rate of 18 sccm. The plasma apparatus was then turned on at a power of 400W, and the reaction was allowed to proceed for 35 min. After the reaction, vertically grown graphene (VG@CF) was obtained on the carbon cloth.

[0063] S2: 100 mL of concentrated sulfuric acid and 60 mL of concentrated nitric acid were measured to prepare a mixed acid, and then electrochemical oxidation was performed at a potential of 3 V (vs. SCE) using an electrochemical workstation, with a VG@CC as a working electrode, a platinum wire as a counter electrode, an SCE as a reference electrode, and the mixed acid as an electrolyte, the oxidation temperature was 25 DEG C, and the oxidation time was 17 min. After the reaction was completed, the reaction solution was washed with deionized water until it was neutral, and finally dried at 60 DEG C for 12 h to obtain the surface-modified VG@CF.

[0064] When the modified vertical graphene prepared in Example 5 was subjected to electrochemical performance testing, the specific capacitance was 1836 mF / cm 2 when the current density was 1 mA / cm 2 , showing super-high capacitive performance.

[0065] The above-described examples only express the preferred embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that, for those skilled in the art, various corresponding changes and modifications can be made to the above-described technical solutions and concepts, and all of these changes and modifications should be within the scope of protection of the claims of the present application.

Claims

1. A method for vertical graphene surface modification for flexible supercapacitor electrodes, characterized by, The method comprises the following steps: S1: growing vertical graphene on a carbon material as a substrate by plasma enhanced chemical vapor deposition; S2: placing the vertical graphene into a concentrated acid mixed solution; the concentrated acid mixed solution comprises concentrated nitric acid and concentrated sulfuric acid, and the volume ratio of the concentrated nitric acid to the concentrated sulfuric acid is 1:1-2.5; S3: then oxidizing the vertical graphene by an electrochemical oxidation method with the concentrated acid mixed solution as an electrolyte; the electrochemical oxidation method is a constant voltage method, the voltage is 3 V, and the oxidation time of the constant voltage method is 5-20 min; S4: finally, washing the oxidized vertical graphene to neutral and performing drying treatment to obtain modified vertical graphene.

2. The method for surface modification of vertical graphene for flexible supercapacitor electrodes according to claim 1, wherein, In step S1, the carbon material comprises at least one of carbon cloth, carbon paper, carbon fiber and carbon nanotube.

3. The method for vertical graphene surface modification for flexible supercapacitor electrodes according to claim 1, wherein, In step S1, the plasma generation device in the plasma enhanced chemical vapor deposition method comprises a microwave plasma or a radio frequency plasma emission device.

4. The method for vertical graphene surface modification for flexible supercapacitor electrodes according to claim 1, wherein, In step S4, the drying temperature is 40-80 ℃, and the drying time is 6-24 h.

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