Preparation Of Nitrogen-Doped Graphene/Polyaniline Composites And Their Applications In Supercapacitors

Supercapacitors have attracted extensive attention due to their excellent cycle life and power density.Electrode materials,as an important part of supercapacitors,determine the overall performance of the devices.The electrode materials studied at present mainly include carbon material,conductive polymer,transition metal oxide and hydroxide.Because different kinds of electrode materials have their own advantages and disadvantages,it is impossible to use a single electrode material in the supercapacitor to achieve the optimal electrochemical performance.Therefore,by combining different kinds of electrode materials,the electrochemical performance can be optimized.Graphene is an ideal electrode material with high electrical conductivity,excellent electrochemical stability and large specific surface area.Heteroatomic doping can adjust its electronic structure to effectively improve its physical and chemical properties.However,the preparation process of graphene is easy to aggregate and accumulate,leading to the reduction of specific surface area and affecting electrochemical properties.Although polyaniline has a high conductivity as the electrode material of supercapacitor,it is easy to expand and contract in the process of charging and discharging,which leads to a significant decline in the electrochemical performance of polyaniline.Therefore,a nitrogen-doped graphene and polyaniline nanocomposite was designed in this paper to take full advantage of the synergistic effect of the composite materials for the purpose of obtain more outstanding electrochemical properties.The results as follow:?1?Conductive polyaniline was synthesized by dilution in-situ polymerization with persulfate amine(NH₄2)S₂O₄ as oxidant,hydrochloric acid?HCl?,sulfuric acid?H₂SO₄?and perchloric acid?HCl O₄?as dopants.SEM results showed that the polyaniline doped with perchloric acid had nanofiber structure and the polyaniline doped with hydrochloric acid and sulfuric acid had nanorod structure.X-ray diffraction spectroscopy and FTIR infrared spectroscopy showed that the three kinds of acid-doped conductive polyaniline were successfully synthesized,and the perchlorate-doped polyaniline was more crystalline than hydrochloric acid and sulfuric acid-doped polyaniline.The electrical conductivity of pani-hclo4 doped with perchloric acid was investigated through four-probe test.The results indicated that PANI-HCl O₄ had the highest electrical conductivity,reaching 10.25 S/cm under the optimal synthesis conditions,higher than PANI-HCl?9.24 S/cm?and PANI-H₂SO₄?8.37 S/cm?.?2?Three-dimensional nitrogen-doped nitrogen-doped graphene hydrogels were prepared by hydrothermal method with ethylenediamine as the nitrogen source and reducing agent.Scanning?SEM?and transmission electron microscope?TEM?showed that the prepared nitrogen-doped graphene had a three-dimensional porous structure,and the nitrogen-doped graphene nanometer sheet was very thin,which also indicated that nitrogen-doped graphene had a large specific surface area.Raman spectroscopy and X-ray diffraction studies have shown that compared with pure graphene,nitrogen-doped graphene materials have increased disorder and layer spacing.The capacitive properties of nitrogen-doped graphene hydrogels were investigated by cyclic voltammetry?CV?,constant-current charge and discharge?GCD?and electrochemical impedance testing?EIS?.The results showed that the material has excellent electrochemical performance,the specific capacitance reaches 317 F g^-1when the current density is 0.5 A g^-1,and reaches130 F g^-1at the current density of 20 A g^-1,with good capacitance behavior.?3?Nitrogen-doped graphene and polyaniline nanocomposites?NG/PANI?were synthesized by dilution in-situ polymerization.Due to the synergistic effect of nitrogen-doped graphene and polyaniline array,the electrochemical performance of NG/PANI is greatly improved compared with that of NG and PANI alone.The specific capacitance of NG/PANI reaches 620 F g^-1at a current density of 0.5 A g^-1,and still reaches 474 F g^-1at A high current density of 20 A g^-1,indicating that NG/PANI composite material has a good multiplier performance.High capacitance of 84.4%was maintained after 5000 cycle stability tests.When the power density of the assembled asymmetric device NG/PANI//AC?ASC?is 800 W kg^-1,the energy density is as high as 33.14 w h kg^-1,5000 cycles with a 79%bottom capacitance retention rate.