A method for preparing high-quality graphene by delocalized electrochemical exfoliation

Abstract

The present invention discloses a method for preparing high-quality graphene by delocalized electrochemical stripping, comprising the following steps: placing a metal anode and a platinum sheet as an anode and a cathode, respectively, into an electrolyte for electrochemical stripping of graphene, with the positive and negative electrodes spaced and extending into the bottom of the electrolyte to form an electrolytic cell structure; adding graphite to the electrolyte, electrolyzing at a constant voltage of 10 to 50 V under stirring until the graphite in the solution is completely stripped, washing, and dispersing to obtain a dispersion of graphene. The present invention achieves efficient preparation of high-yield, low-defect graphene, pushes the efficiency of electrochemical stripping and the quality of graphene to a new height, and accelerates the large-scale batch preparation and commercial application of high-quality graphene.

Description

Technical Field

[0001] The invention belongs to the technical field of graphene preparation, and in particular relates to a method for preparing high-quality graphene by delocalized electrochemical exfoliation. Background Art

[0002] Since graphene was first reported in 2004, it has been extensively and deeply studied by the scientific and industrial communities. It has great application potential in energy storage, seawater purification, anti-corrosion materials, catalysis, biomedical engineering, detectors, etc. Developing efficient methods to prepare high-quality graphene is crucial to promote the commercial application of graphene. The current challenges faced by the methods of preparing high-quality graphene are two factors that need to be guaranteed at the same time but seem to be incompatible, namely the integrity of the graphite structure and the exfoliation efficiency.

[0003] The electrochemical exfoliation method is considered to be the most promising method for the large-scale preparation of high-quality graphene. In this method, the potential provides green and safe conditions, driving the embedding of charged particles into graphite and generating bubbles between the graphite layers to produce exfoliation. The existing electrochemical method uses graphite as the cathode and / or anode electrode, and the ion intercalation formed by the electrode potential and the exfoliation of graphite depend on the electrical contact between the graphite electrode and the power supply. At the same time, the bubbles generated during the electrode reaction will inevitably damage the graphite electrode and cause it to fall off. As a result, many graphite particles will separate from the electrode and lose electrical contact with the electrode before deep exfoliation occurs. This makes it difficult for existing electrochemical methods to further improve the yield and preparation efficiency of graphene. In addition, the traditional electrochemical method can only use the potential on the graphite electrode to produce exfoliation. Although the high potential can promote the exfoliation speed, it will cause the anode graphene to oxidize and cause structural damage, so it cannot solve the competitive relationship between the quality and production efficiency of graphene.

[0004] In summary, the current electrochemical methods for preparing graphene have the above shortcomings, and it is difficult to achieve efficient deep exfoliation to produce graphene with few / no defects, which is not conducive to promoting the large-scale preparation of high-quality graphene. Summary of the invention

[0005] The purpose of the present invention is to overcome the technical defects of the existing electrochemical stripping method and provide a method for preparing high-quality graphene by delocalized electrochemical stripping, which can ensure high-efficiency stripping and achieve non-destructive destruction of the structure, and the process is easy to scale up and continuously strip graphene.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing high-quality graphene by delocalized electrochemical exfoliation comprises the following steps:

[0008] A metal anode and a platinum sheet are used as an anode and a cathode respectively, and are placed in an electrolyte for electrochemical exfoliation of graphene. The positive and negative electrodes are arranged at intervals and extend to the bottom of the electrolyte to form an electrolytic cell structure.

[0009] Graphite is added to the electrolyte, and electrolysis is performed at a constant voltage of 10 to 50 V under stirring until the graphite in the solution is completely peeled off, washed, and dispersed to obtain a graphene dispersion.

[0010] Furthermore, the electrolyte for electrochemical exfoliation of graphene is prepared by the following process: one or more of tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate and tetrabutylammonium perchlorate are used as solutes, and a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 is used as a solvent, and the solute and the solvent are evenly mixed to obtain the electrolyte.

[0011] Furthermore, the molar concentration of the solute in the electrolyte is 0.01-1 mol / L.

[0012] Furthermore, the electrolyte also includes additives.

[0013] Furthermore, the additive is one or more of lithium hexafluorophosphate, lithium tetrafluorophosphate and lithium ammonium perchlorate.

[0014] Furthermore, the molar concentration of the additive is 0.001-0.01 mol / L.

[0015] Furthermore, the graphite is natural flake graphite, microcrystalline graphite, artificial graphite, highly oriented pyrolytic graphite, graphite rod or graphite foil.

[0016] Furthermore, the electrolysis time is 50-100 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention places dispersed graphite particles in a traditional electrolytic cell device. Under the action of the voltage between the cathode and anode electrodes, a uniform electric field distribution is generated in the electrolytic cell, and an oxidation and reduction potential gradient is formed at both ends of the graphite particles placed therein, thereby inducing synchronous anion and cation intercalation and exfoliation reactions of the graphite in the solution. The present invention delocalizes the graphite exfoliation process generated at the interface of the traditional electrode / electrolyte to the entire electrolyte system, suspends the graphite in the solution, and under the action of a strong electric field, ions will be embedded in the graphite suspended in the solution and exfoliation will occur. By designing an electrolyte with excellent electrochemical stability, deep and non-destructive bipolar efficient exfoliation of each graphite particle dispersed in the electrolyte is achieved, and the structural integrity of the graphene and the excellent production speed are ensured. In addition, this exfoliation method is easier to achieve continuous exfoliation and is convenient for scaled-up production. This bipolar electrochemical exfoliation strategy completely changes the existing method of electrochemical exfoliation of graphite, and improves the quality of the obtained graphene (defect density is between I d / I g <0.05), yield (>95%), and energy utilization (compared with traditional stripping methods, the stripping efficiency can be increased by more than 30%), achieving the efficient preparation of high-yield, low-defect graphene, pushing the efficiency of electrochemical stripping and the quality of graphene to a new level, and accelerating the large-scale batch preparation and commercial application of high-quality graphene. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the comparison of the process principle of conventional electrochemical cation-cation bipolar synchronous exfoliation of graphene and bipolar electrochemical cation-cation bipolar synchronous exfoliation of graphene. Among them, (a) is conventional electrochemical cation-cation bipolar synchronous exfoliation of graphene, and (b) is bipolar electrochemical cation-cation bipolar synchronous exfoliation of graphene.

[0020] Figure 2 This is a diagram showing the phenomenon of bipolar electrochemical anode- cathode bipolar exfoliation of graphite foil in an electrolyte composed of tetrabutylammonium hexafluorophosphate (TBAPF6) and lithium hexafluorophosphate (LiPF6).

[0021] Figure 3 Figure 2 shows the actual dispersion of graphene exfoliated in large quantities by bipolar electrochemical method (dispersion concentration is 1 g L -1 , volume is 20 L, total 20 g).

[0022] Figure 4 This is a scanning electron microscope image of graphene.

[0023] Figure 5 The high-resolution transmission electron microscopy images of graphene, where (a) is a high-resolution transmission electron microscopy image of a single-layer graphene, and (b) is a high-resolution transmission electron microscopy image of a double-layer graphene.

[0024] Figure 6 Comparison of Raman spectra of graphene and natural graphite used. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings.

[0026] The method for preparing graphene of the present invention comprises the following steps:

[0027] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0028] A mixture of one or more of tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate and tetrabutylammonium perchlorate with excellent electrochemical stability is used as the solute; a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 (the three are liquid, so they are measured in a volume ratio) is used as the solvent;

[0029] After the solute and the solvent are mixed, in order to increase the conductivity of the solution and improve the stripping efficiency of the anions at the anode end of the graphite sheet, a small amount of one or more substances selected from lithium hexafluorophosphate, lithium tetrafluorophosphate and lithium ammonium perchlorate are added to the mixed solution as additives; then stirred on a magnetic stirrer to form a completely dissolved transparent solution as an electrolyte for electrochemical stripping of graphene. The molar concentration of the solute in the electrolyte for electrochemical stripping of graphene is 0.01-1 mol / L, and the molar concentration of the additive is 0.001-0.01 mol / L.

[0030] (2) Continuous exfoliation process of graphene:

[0031] 2.1 Take a dimensionally stable metal anode (a coating of ruthenium oxide or titanium oxide crystals on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 50-200 mL of electrolyte for electrochemical exfoliation of graphene, and place the positive and negative electrodes 3-5 cm apart and fully extend to the bottom of the electrolyte to form an electrolytic cell structure.

[0032] 2.2 Add 0.01-1 g of graphite per 1 mL of electrolyte, add the weighed graphite to the electrolyte, and stir with a magnetic bar at a stirring speed of 50-500 rpm.

[0033] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and electrolyze at a constant voltage of 10 to 50 V for a sufficient period of time (50 to 100 h) until all the graphite in the solution is completely stripped off.

[0034] 2.4 Continuous reaction: After the reaction is completed, the completely exfoliated graphene is scooped out with a mesh, and new graphite is added to the electrolyte. The electrochemical reactions of steps 2.2 and 2.3 are repeated to achieve continuous exfoliation of graphene until 100-500 g of product is obtained.

[0035] (3) Graphene cleaning process:

[0036] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0037] 3.2 The washed graphene filter cake is dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion is then centrifuged in a centrifuge at a rate of 2000-5000 rpm for 30 min, and the upper layer is extracted and preserved to obtain the graphene dispersion.

[0038] The graphite in the step may include not only natural flake graphite but also microcrystalline graphite, artificial graphite, highly oriented pyrolytic graphite, graphite rod or graphite foil.

[0039] Example 1

[0040] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0041] A mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; 0.1 mol / L tetrabutylammonium hexafluorophosphate (TBAPF6) is used as a solute; 0.01 mol / L lithium hexafluorophosphate (LiPF6) is used as an additive to improve the conductivity of the solution; the weighed solute and additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene.

[0042] (2) Graphene exfoliation process:

[0043] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 100 mL of electrolyte for electrochemical exfoliation of graphene (0.1 mol / L TBAPF6 + 0.01 mol / L LiPF6), the positive and negative electrodes are 3 cm apart and completely extend to the bottom of the electrolyte, thus forming an electrolytic cell structure.

[0044] like Figure 2 As shown, placing a piece of graphite foil as a graphite source in a solution can achieve the phenomenon of bipolar exfoliation of graphite in the solution, which confirms the feasibility of using the delocalized electrochemical cation-cation bipolar exfoliation method of the present invention.

[0045] 2.2 In order to more efficiently exfoliate graphite and increase the density of graphite in the solution, natural graphite flake graphite is used as the graphite source, 20 g of graphite is weighed, the weighed graphite is added to the above electrolyte, and stirred with a magnet at a stirring speed of 100 rpm.

[0046] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and perform electrolysis at a constant voltage of 50 V for 60 h until all the graphite in the solution is completely stripped off.

[0047] (3) Graphene cleaning process:

[0048] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0049] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 2000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0050] from Figure 3 It can be seen that with 20 g of graphite as the starting material, the mass of stable graphene produced after exfoliation is close to 20 g (the dispersion concentration is ~1 g L -1 , volume 20 L, total 20 g), the yield is as high as over 95%, which is significantly improved compared with the traditional method (traditional method <80%).

[0051] At the same time by Figure 4 It can be seen that the graphene nanosheets prepared by this method present a thin layer morphology, and the sheet diameter is mainly between 3-6 microns.

[0052] from Figure 5 It can be seen from (a) and (b) that the prepared graphene contains single-layer and double-layer graphene.

[0053] It is important that the graphene prepared by the present invention has excellent quality. Figure 6 It can be seen that the defect density ( I D / I G ) is only 0.045, which is only a small increase compared to natural graphite. The optimal defect density of graphene prepared by the existing electrochemical method is also greater than 0.05, indicating the outstanding advantages of the bipolar electrochemical method of the present invention in preparing high-quality graphene.

[0054] Example 2

[0055] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0056] A mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; tetrabutylammonium tetrafluoroborate is used as a solute; and lithium tetrafluorophosphate is used as an additive for improving the conductivity of the solution. The solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene. The solute concentration in the electrolyte is 0.01 mol / L, and the concentration of the additive is 0.001 mol / L.

[0057] (2) Graphene exfoliation process:

[0058] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 50 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 3 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0059] 2.2 Add natural graphite flake graphite to the above electrolyte and stir it with a magnet at a stirring speed of 100 rpm, wherein 0.01 g of natural graphite flake graphite is added to 1 mL of electrolyte.

[0060] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and electrolyze at a constant voltage of 10 V for 100 h until all the graphite in the solution is completely stripped off.

[0061] (3) Graphene cleaning process:

[0062] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0063] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 2000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0064] Example 3

[0065] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0066] A mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; tetrabutylammonium hexafluorophosphate is used as a solute; and lithium ammonium perchlorate is used as an additive for improving the conductivity of the solution. The solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene. The solute concentration in the electrolyte is 0.1 mol / L, and the concentration of the additive is 0.01 mol / L.

[0067] (2) Graphene exfoliation process:

[0068] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 100 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 4 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0069] 2.2 Add microcrystalline graphite to the above electrolyte and stir it with a magnet at a stirring speed of 200 rpm, wherein 1 g of microcrystalline graphite is added to 1 mL of electrolyte.

[0070] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and perform electrolysis at a constant voltage of 50 V for 50 h until all the graphite in the solution is completely stripped off.

[0071] (3) Graphene cleaning process:

[0072] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0073] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 2000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0074] Example 4

[0075] A mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; tetrabutylammonium perchlorate is used as a solute; a mixture of lithium ammonium perchlorate and lithium tetrafluorophosphate is used as an additive to improve the conductivity of the solution; the solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene, the solute concentration in the electrolyte is 1 mol / L, and the concentration of the additive is 0.005 mol / L.

[0076] (2) Graphene exfoliation process:

[0077] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 200 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 5 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0078] 2.2 Add artificial graphite to the above electrolyte and stir it with a magnet at a stirring speed of 300 rpm, wherein 0.05 g of artificial graphite is added to 1 mL of electrolyte.

[0079] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and electrolyze at a constant voltage of 70 V for 70 h until all the graphite in the solution is completely stripped off.

[0080] (3) Graphene cleaning process:

[0081] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0082] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 2000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0083] Example 5

[0084] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0085] A mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; a mixture of tetrabutylammonium hexafluorophosphate and tetrabutylammonium perchlorate is used as a solute; a mixture of lithium hexafluorophosphate (LiPF6) and lithium tetrafluorophosphate is used as an additive to improve the conductivity of the solution; the solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene, the solute concentration in the electrolyte is 0.5 mol / L, and the concentration of the additive is 0.005 mol / L.

[0086] (2) Graphene exfoliation process:

[0087] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 150 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 3 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0088] 2.2 Add highly oriented pyrolytic graphite to the above electrolyte and stir with a magnet at a speed of 400 rpm, wherein 0.1 g of highly oriented pyrolytic graphite is added to 1 mL of electrolyte.

[0089] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and perform electrolysis at a constant voltage of 80 V for 60 h until all the graphite in the solution is completely stripped off.

[0090] (3) Graphene cleaning process:

[0091] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0092] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 5000 rpm for 30 min, and the upper layer was extracted and preserved to obtain the graphene dispersion.

[0093] Example 6

[0094] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0095] A mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; a mixture of tetrabutylammonium tetrafluoroborate and tetrabutylammonium hexafluorophosphate is used as a solute; a mixture of lithium hexafluorophosphate (LiPF6), lithium tetrafluorophosphate and lithium ammonium perchlorate is used as an additive to improve the conductivity of the solution; the solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene, the solute concentration in the electrolyte is 0.7 mol / L, and the concentration of the additive is 0.008 mol / L.

[0096] (2) Graphene exfoliation process:

[0097] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 120 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 3 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0098] 2.2 Add the graphite rod to the above electrolyte and stir with a magnet at a stirring speed of 50 rpm, wherein 0.5 g of graphite rod is added to 1 mL of electrolyte.

[0099] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and electrolyze at a constant voltage of 50 V for 100 h until all the graphite in the solution is completely stripped off.

[0100] (3) Graphene cleaning process:

[0101] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0102] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 3000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0103] Example 7

[0104] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0105] A mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; 0.1 mol / L tetrabutylammonium hexafluorophosphate (TBAPF6) is used as a solute; lithium hexafluorophosphate (LiPF6) is used as an additive to improve the conductivity of the solution; the solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene. The solute concentration in the electrolyte is 0.01 mol / L, and the concentration of the additive is 0.01 mol / L.

[0106] (2) Graphene exfoliation process:

[0107] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 180 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 3 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0108] 2.2 Add graphite foil to the above electrolyte and stir with a magnet at a stirring speed of 300 rpm, wherein 0.8 g of graphite foil is added to 1 mL of electrolyte.

[0109] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and electrolyze at a constant voltage of 65 V for 66 h until all the graphite in the solution is completely stripped off.

[0110] (3) Graphene cleaning process:

[0111] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0112] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 2000 rpm for 30 min, and the upper layer was extracted and stored to obtain the graphene dispersion.

[0113] Example 8

[0114] (1) Prepare an electrolyte for electrochemical exfoliation of graphene, the formula of which is as follows:

[0115] A mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of the three: 1:1:1) is used as a solvent; 0.1 mol / L tetrabutylammonium hexafluorophosphate (TBAPF6) is used as a solute; lithium hexafluorophosphate (LiPF6) is used as an additive to improve the conductivity of the solution; the solute and the additive are dissolved in the solvent and stirred on a magnetic stirrer to form a completely dissolved transparent solution, which is used as an electrolyte for electrochemical exfoliation of graphene. The solute concentration in the electrolyte is 0.03 mol / L, and the concentration of the additive is 0.004 mol / L.

[0116] (2) Graphene exfoliation process:

[0117] 2.1 Take a dimensionally stable metal anode (ruthenium oxide plated on a metal titanium sheet) and a platinum sheet as the anode and cathode respectively, take 70 mL of electrolyte for electrochemical exfoliation of graphene, and the positive and negative electrodes are 3 cm apart and fully extended to the bottom of the electrolyte to form an electrolytic cell structure.

[0118] 2.2 Add natural graphite flake graphite to the above electrolyte and stir with a magnet at a stirring speed of 500 rpm, wherein 0.01 g of natural graphite flake graphite is added to 1 mL of electrolyte.

[0119] 2.3 Connect the power supply to the cathode and anode, turn on the power supply, and perform electrolysis at a constant voltage of 35 V for 85 h until all the graphite in the solution is completely stripped off.

[0120] (3) Graphene cleaning process:

[0121] 3.1 Use ultrapure water and ethanol to filter and clean the peeled graphene multiple times (more than 5 times) to remove impurities such as electrolyte.

[0122] 3.2 The washed graphene filter cake was dispersed in N, N-dimethylformamide organic solvent and ultrasonicated in an ultrasonicator for 30 min. The graphene dispersion was then centrifuged in a centrifuge at a rate of 5000 rpm for 30 min, and the upper layer was extracted and preserved to obtain the graphene dispersion.

[0123] like Figure 1 As shown in (a), the traditional dual-electrode stripping process uses graphite as the cathode and anode respectively. The stripping phenomenon can only occur on the electrodes. The graphite detached from the electrodes will no longer produce ion intercalation and stripping, resulting in low yield and low energy utilization. The preparation method of the present invention delocalizes the graphite stripping process generated at the traditional electrode / electrolyte interface to the entire electrolyte system. Figure 1 As shown in (b), graphite is suspended in a solution. Under the action of a strong electric field, ions will be embedded in the graphite suspended in the solution and exfoliation will occur. By designing an electrolyte with excellent electrochemical stability, the electrolyte can achieve bipolar exfoliation. Therefore, the electrolyte needs to have high electrochemical stability, otherwise bipolar exfoliation cannot be achieved. The reason for the excellent performance here is that the traditional electrode exfoliation is delocalized into the entire electrolyte, that is, exfoliation can always occur in the electrolyte. Therefore, the degree of exfoliation of graphene is high and the yield of the product is high, thereby achieving deep and non-destructive bipolar efficient exfoliation of each graphite particle dispersed in the electrolyte, and ensuring the structural integrity of graphene and excellent production speed. In addition, this exfoliation method is easier to achieve continuous exfoliation and is convenient for scale-up production. This bipolar electrochemical stripping strategy completely changes the existing way of electrochemically stripping graphite (this delocalized stripping method affects the yield of the product. In the traditional stripping method, graphite will not continue to strip after it is separated from the electrode, so the product yield is low and leads to low energy utilization. In addition, the oxidation on the electrode causes more defects in the product; the stripping method of the present invention is to electrochemically strip graphite in a solution, which is achieved by suspending graphite powder in a solution by stirring. Under the action of the strong electric field generated by the high voltage on the two electrodes, a potential difference is generated on each graphite powder in the solution, thereby causing ion intercalation and stripping, so that the graphite in the solution can be stripped, so the degree of graphite stripping is high and the yield is also high; at the same time, since the potential allocated to each graphite is not very large, the defect density of the product is low; compared with traditional electrodes that can only strip graphite on the electrode, the present invention can strip all graphite dispersed in the solution, so the energy utilization rate is also greatly improved), and improves the quality of the obtained graphene (the defect density is in I d / I g<0.05), yield (>95%), and energy utilization (compared with traditional stripping methods, the stripping efficiency can be increased by more than 30%), achieving the efficient preparation of high-yield, low-defect graphene, pushing the efficiency of electrochemical stripping and the quality of graphene to a new level, and accelerating the large-scale batch preparation and commercial application of high-quality graphene.

[0124] The present invention is different from the traditional electrochemical method of using graphite as the cathode and anode electrodes to perform stripping at the electrode / electrolyte interface, but proposes a delocalized electrochemical stripping method. The process is to use a platinum sheet and a shape-stable anode as the cathode and anode electrodes of the electrolytic cell, respectively, disperse graphite particles in the electrolyte, select an electrolyte with a wide electrochemical window, and realize that the anions and cations are respectively embedded in the two poles of the monomer graphite in the solution, thereby delocalizing the graphite stripping process from the traditional electrode to the entire electrolyte system. The present invention can not only enable each graphite particle dispersed in the solution to be deeply stripped, thereby greatly improving the production efficiency of graphene, but also effectively avoid oxidation, continuous stripping at low cost, and can achieve large-scale, stable and efficient preparation of high-quality graphene. The method for stripping graphene provided by the present invention will promote the large-scale preparation and wide application of graphene and even other two-dimensional materials.

Claims

1. A method for preparing high-quality graphene by delocalized electrochemical exfoliation, characterized in that: The following steps are involved: A metal anode and a platinum sheet are used as an anode and a cathode respectively, and are placed in an electrolyte for electrochemical exfoliation of graphene. The positive and negative electrodes are arranged at intervals and extend to the bottom of the electrolyte to form an electrolytic cell structure. Add graphite to the electrolyte, electrolyze at a constant voltage of 10 to 50 V under stirring until the graphite in the solution is completely peeled off, washed, and dispersed to obtain a graphene dispersion; The electrolyte for electrochemical exfoliation of graphene is prepared by the following process: one or more of tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate and tetrabutylammonium perchlorate are used as solutes, and a mixture of ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1:1:1 is used as a solvent, and the solute and the solvent are uniformly mixed to obtain the electrolyte; The molar concentration of the solute in the electrolyte is 0.01-1 mol / L.

2. The method for preparing high-quality graphene by delocalized electrochemical exfoliation according to claim 1, characterized in that: The electrolyte also includes additives.

3. The method for preparing high-quality graphene by delocalized electrochemical exfoliation according to claim 2, characterized in that: The additive is one or more of lithium hexafluorophosphate, lithium tetrafluorophosphate and lithium ammonium perchlorate.

4. The method for preparing high-quality graphene by delocalized electrochemical exfoliation according to claim 3, characterized in that: The molar concentration of the additive is 0.001-0.01 mol / L.

5. The method for preparing high-quality graphene by delocalized electrochemical exfoliation according to claim 1, characterized in that: The graphite is natural flake graphite, microcrystalline graphite, artificial graphite, highly oriented pyrolytic graphite, graphite rod or graphite foil.

6. The method for preparing high-quality graphene by delocalized electrochemical exfoliation according to claim 1, characterized in that: The electrolysis time is 50-100 h.

Images