The graphene grafted polypyrrole composite was synthesized in situ by chemical grafting, and the structure, morphology, conductivity and specific capacitance of the composite were tested and characterized.

　　The results show that in the prepared graphene-grafted polypyrrole composite, the graphene and the pyrrole monomer have a close chemical bond. The pyrrole is evenly distributed on the graphene layers, and the pyrrole between the graphene layers is formed into chains in a large amount and interacts with the graphite. The olefin layers are connected to each other. The measured conductivity of the composite is 3.32S/cm, and the specific capacitance can reach 284F/g. Compared with the 186F/g of pure polypyrrole, the specific capacitance is increased by 52%, which is excellent Capacitance characteristics.

　　Polypyrrole (PPy) is a typical conductive polymer material. It has the advantages of simple synthesis process, low cost, high oxidation resistance, high conductivity and specific capacitance, and easy film formation. It is an ideal electrode material for preparing supercapacitors. .

　　Graphene has ultra-high electrical conductivity, excellent mechanical properties and thermal stability, as well as a huge specific surface area, which can provide enough electrochemical reaction active area for polypyrrole; its huge specific surface area and abundant functional groups on the surface, and polymer The composite has a significant improvement effect on the capacitance characteristics of the polymer. Therefore, the polypyrrole/graphene composite with graphene as the matrix has attracted widespread attention as the electrode material of the supercapacitor. According to literature reports, pyrrole and graphene oxide (GO) are polymerized in situ with ammonium peroxodisulfate ((NH4)S2O8) to form a polypyrrole/graphene oxide composite, and then GO is reduced to graphene by NaBH4 to synthesize For the polypyrrole/graphene composite, tested in 1mol/LH2SO4 electrolyte, the specific capacitance of polypyrrole/graphene is up to 180F/g. It is also reported that the graphene oxide is dispersed into the electrolyte system by the direct current electrodeposition method. During the polymerization process, the PPy structure wraps the graphene fragments to prepare a polypyrrole/graphene composite with a specific capacitance value of up to 229F/g .

　　Although people have conducted a lot of research on the composite of graphene and polypyrrole, there are few reports on how to effectively realize the chemical bonding of graphene and polypyrrole to construct a stable electron transfer channel, thereby improving the capacitance characteristics of the material. In this work, an in-situ synthesis method was used to prepare graphene grafted polypyrrole composite (GPPy), and the surface-modified graphene oxide was acylated with thionyl chloride to introduce the active polar group acid chloride group (–COCl). ) To react with the pyrrole monomer (Py) to form an amide bond -CON<, so as to achieve the purpose of grafting. The chemical bond generated between polypyrrole and graphene sheet layer by grafting serves as a stable carrier channel between the two, which can greatly increase the electron transfer rate during the electrochemical oxidation-reduction reaction of polypyrrole, increase the reaction efficiency of PPy, and optimize The tightness of the combination of PPy and the graphene matrix prevents the material from peeling and separation caused by the reaction and affects the stability of the specific capacitance, thereby greatly improving the specific capacitance of the electrode material.

　　1, experiment

　　1.1, experimental materials

　　Hydrated ferric chloride (FeCl3·6H2O, analytically pure) is produced by Tianjin Yaohua Chemical Plant; Thionyl chloride (SOCl2, analytically pure) is produced by Xilong Chemical Co., Ltd.; 80% hydrated hydrazine (N2H4·H2O, Analytical grade) is produced by Guangdong Guanghua Technology Co., Ltd.; pyrrole (C4H5N, chemically pure) is produced by Sinopharm Chemical Reagent Co., Ltd.; N,N-dimethylformamide (DMF, analytically pure) is produced by Xilong Chemical Co., Ltd. Production, graphite oxide powder is prepared by Hummer method from natural flake graphite powder produced by Qingdao Laixi Graphite Colloid Factory.

　　1.2. Preparation of graphene grafted polypyrrole composite

　　Weigh 0.1g graphite oxide powder, grind it and place it in 2mL DMF for ultrasonic dispersion for 15 minutes, and pour the dispersed graphite oxide (GO) into a three-necked flask, add 20mL of thionyl chloride to it, ice bath and stir for 2h . After the reaction, the remaining thionyl chloride was blown dry with nitrogen at 80°C in an oil bath, and then 2 mL of pyrrole monomer (Py) solution dissolved in 50 mL of deionized water was poured into a three-necked flask, and the temperature was controlled to 0 ℃ ice bath and stir the reaction for 30min. Weigh 3.8g of FeCl3·6H2O to prepare 50mL of FeCl3 solution, pour into a three-necked flask, continue to ice bath and stir, after reacting for 6h, wash with a mixed solution of ethanol and deionized water and filter. Place the filter block in a constant temperature drying box to control the temperature at 60℃ to dry, reduce the dried powder with water and hydrazine, stand for 12 hours, wash and filter with a mixed solution of ethanol and deionized water, and place the obtained filter block at 60°C. Dry in a constant temperature drying oven at ℃ to obtain GPPy.

　　In order to compare the structure and electrochemical characteristics of graphene grafted polypyrrole material and its separate components graphene and polypyrrole, the experiment also used hydrazine hydrate to reduce graphite oxide to prepare pure graphene material (G), and it will contain 2mL A 50mL aqueous solution of pyrrole monomer and a 50mL FeCl3 solution containing 3.8g FeCl3·6H2O were directly mixed and ice-bathed for 6 hours to prepare pure PPy materials. G and PPy materials were used as comparison samples.

　　1.3, analysis and testing methods

　　Use an X-ray diffractometer (Rigaku, CuKα, λ=0.15418nm, working voltage 40kV, current 40mA) to analyze the structure of the sample, with a scanning range of 5°~70°, and a scanning speed of 5°/min. Use AVATAR360FT-IR, Nicelet infrared spectrometer to test and analyze the sample by infrared spectroscopy. A laser confocal Raman spectrometer (LabRAMHR800, helium-neon laser, wavelength of 632.8nm) was used to perform Raman spectroscopy on the samples. Scanning electron microscope (XL30S-FEG, SIRION, JAPAN) and transmission electron microscope (JEOLJEM-2100) were used to observe the morphology and structure of the sample. The SZT-D semiconductor powder conductivity test bench is used to test the conductivity of powder samples. The constant current charge and discharge test was carried out on Chenhua CHI660a electrochemical workstation. When the three-electrode chronopotentiometry is used to test the specific capacitance value, the glassy carbon electrode is used as the working electrode, the Ag/AgCl electrode (SCE) is used as the reference electrode, and the platinum electrode is used as the counter electrode. The electrolyte for all tests is a 2mol/L H2SO4 aqueous solution.

　　2. Results and discussion

　　2.1, SEM scanning electron microscope analysis

　　The graphene prepared by reducing graphene oxide with hydrazine hydrate and ultrasonically dispersing it (Figure 1(b)) has a good layer structure, with a smooth surface and smooth edges. This is because graphene oxide undergoes SOCl2 acid chlorination modification treatment to introduce a large number of acid chloride groups on the edge and surface, and the added pyrrole undergoes polymerization under the oxidation of FeCl3, and part of the pyrrole monomer at the end of the pyrrole chain and The modified intermediate product of graphene oxide with acid chloride groups undergoes an electrophilic substitution reaction to form an amide bond, and then the graphene oxide is reduced to graphene by hydrazine hydrate, and the graphene and polypyrrole are firmly linked through the amide bond. Generate graphene grafted polypyrrole composite. As the graphene oxide sheet has undergone the SOCl2 acyl chloride modification treatment, the electrophilic reaction between pyrrole and the acid chloride group, and the subsequent hydrazine hydrate reduction treatment, its surface morphology has changed significantly, and the original smooth surface has a large number of irregularities. Evenly undulating, there are a large number of PPy-shaped particles on the edge of the graphene layer. It is difficult to distinguish the boundary between PPy and graphene. This also shows that graphene and polypyrrole are tightly bound together through amide bonds. It can be seen from Figure 1(d) that the pyrrole is polymerized into chains in the middle of the graphene sheets, and the graphene sheets are connected together, which indicates that graphene and polypyrrole are effectively bridged through amide bonds.

　　in conclusion

　　The graphene grafted polypyrrole composite was successfully synthesized in situ by chemical grafting. The structure and morphology studies showed that the pyrrole monomer was connected to the graphene layer by amide bond, and the pyrrole was evenly distributed on the graphene layer. The pyrrole between the graphene sheets forms a large number of chains and connects with the graphene sheets. The synergistic effect of graphene and polypyrrole greatly increases the conductivity of the composite relative to pyrrole, from 0.22S/cm of polypyrrole to 3.32S/cm. The specific capacitance of the graphene grafted polypyrrole composite can reach 284F/g, which is 52% higher than the 186F/g of pure polypyrrole, showing excellent capacitance characteristics.