Study On The Preparation And Electrochemical Performance Of Functionalized Graphene/Polyaniline Composites

Under the condition of traditional non-renewable energy increasing depletion and economy developing rapidly,it is difficult to meet the urgent demands of human society continuously.On the premise of social sustainable development and meeting the principles of energy demand and environmental protection,it is of great strategic significance to reduce the utilization of fossil fuels and develop green,clean and environmental friendly renewable resources and high-efficiency energy storage systems.The efficient conversion and storage of renewable resources is the key issue for new energy industry.What's more,the development of high-performance energy storage components is particularly important for this.Due to the advantages of high power density,environmental protection and long service life,supercapacitors have become an attractive choice in energy storge.Electrode materials,the important part of supercapacitors,play a decisive role in the performance of supercapacitors.Graphene and polyaniline(PANI)are widely used as electrode materials for supercapacitors.Graphene could form an electric double layer over the entire structure to complete the charge and discharge process rapidly,but the theoretical capacity is unsatisfactory.PANI provides pseudocapacitance through undergoing redox reactions on surface and near surface,but its stability needs to be improved.Composite electrode materials with excellent cycle stability and high capacitance are currently the focus of research on electrode materials for supercapacitors.From the aspects of preparation and morphology control of PANI and functionalized graphene along with the adjustment of preparation parameter in composite,a variety of functionalized graphene/polyaniline composites have been prepared.The major research content of this subject is to study the electrochemical performance of single-component and composite materials,analyze the enhancing mechanism of composite materials and explore effective methods to improve the electrochemical performance of materials.PANI was synthesized by chemical oxidation method with ammonium persulfate(APS)as the initiator.The polymerization and doping take place in HCl solution at the same time,and the variable parameters are polymerization temperature and the amount of initiator.Through studying the influence of these two factors on the morphology,conductivity and electrochemical properties of PANI,the relationship between the polymerization technical conditions and performance is systematically analyzed,which could provide a reference for the following preparation of PANI-based composites.With the increase of temperature and initiator,the diameter of PANI gradually increases and the agglomeration with uneven size appears.The specific surface area also reduces,among which the specific surface area of S2 is 58.57 m2/g and 17.3 m2/g for S9.PANI is in a doped state wih excellent conductivity.The conductivity of S1 is 15.5 S/cm PANI exhibits typical pseudocapacitive characteristics,with obvious redox peaks on CV curves.At a current density of 0.6 A/g,the specific capacitance of samples S1-S9 is 301,304,300,300,302,296,275,276 and 251 F/g,respectively.The specific capacitance of samples prepared at 10? and 15? is overall higher than that of 20?.The capacitance of the samples prepared with a molar ratio of APS to aniline as 1 is higher than that of other initiator dosages,indicating that a proper amount of initiator ratio enable PANI a regular structure and excellent performance.Graphene oxide(GO)was prepared by Hummer's method,and then graphene oxide/polyaniline(GO/PANI)composites were achieved in GO suspension via in situ polymerization.Through the analysis of morphology,chemical composition,electrochemical performance and cycle stability of GO/PANI composites,the influence of the amount of aniline monomer was explored.The interplanar spacing of GO is 0.86 nm,and the crystallinity and degree of graphitization are relatively high.In GO/PANI composites,PANI nanorods are attached to the GO sheets to form a tightly arranged sandwich structure.As the amount of aniline increases,the distribution of PANI on the GO surface becomes more uniform,and the coating degree to GO increases,which provides favorable conditions for the improvement of specific capacitance from the structural aspect.The GO/PANI-80 composite exhibits the best electrochemical performance among all samples.The specific capacitance reaches up to 665 F/g at a scan rate of 10 mV/s,and when the current density is 1 A/g,the specific capacitance is 405 F/g.When tested in two-electrode system,the GO/PANI-80 composite shows the specific capacitance of 97 F/g at 1 A/g and the energy density and power density are 13.5 Wh/kg and 251 W/kg,respectively.In addition,the specific capacitance still retains 80.4%at the current density of 6 A/g,exhibiting the enhanced rate capacity.Functionalized reduced graphene oxide(FRGO)was prepared by solvothermal reduction method with NaBH4 as reducing agent in NH3-H2O environment.Functionalized reduced graphene oxide/polyaniline(FRGO/PANI)composites were achieved by synthesizing PAN1 on FRGO substrate via in situ polymerization method.A variety of test methods were carried out to characterize the morphology and electrochemical properties of FRGO and FRGO/PANI composites,explore the effect of FRGO dosage on composite properties and determine appropriate process parameters.The interplanar spacing of FRGO is 0.37 nm and the crystallinity is lower than that of GO.Due to the introduction of N atoms,the surface defects increase and the degree of graphitization decreases.The shape of CV curves for FRGO is rectangular,and the GCD curves are in the shape of symmetrical isosceles triangle.This is a typical electric double layer capacitive feature and the shape does not change regardless of scan rate or current density.The specific capacitance of FRGO is 113 F/g at 0.6 A/g and the specific capacitance is 96 F/g at high current density,showing an excellent rate capability.After the cycle stability test,the capacitance retention rate is 91.6%.The impedance is low and the capacitance performance is outstanding.In FRGO/PANI composites,the PANI nanorod network structure wraps on the FRGO layer.As the amount of FRGO increases,the agglomeration phenomenon fades.FRGO/PANI-30 achieves the best electrochemical performance.The specific capacitance is 421 F/g at 0.6 A/g.The capacitance retention rate is 81.7%in cycle stability test.In FRGO/PANI composites,both electric double layer capacitance and pseudocapacitance make contributions in providing the capacitance and improving the electrochemical stability.Covalent reduced graphene oxide(E-RGO)was prepared by ethylenediamine(EDA)reducing and modifying GO.Covalent reduced graphene oxide/polyaniline(E-RGO/PANI)composites were achieved by synthesizing PANI in different E-RGO suspensions.Through the characterization and analysis of E-RGO and E-RGO/PANI composites,the influence of the amount of EDA on E-RGO and E-RGO/PANI composites was explored and the process conditions for preparing high-performance E-RGO/PANI composites were established.During the reduction process,EDA was introduced to the surface of E-RGO to complete the covalent bond modification of E-RGO.The interplanar spacing of E-RGO is 0.39 nm with the low crystallinity and the XRD diffraction peaks are broad and diffuse.E-RGO embodies the characteristics of electric double layer capacitance.Among them,E-RGO-12 has the best electrochemical performance.At a scan rate of 1 mV/s,the specific capacitance is 170 F/g and at a current density of 0.6 A/g.,the specific capacitance is 102 F/g,which is related to its large surface area and fewer defects.The E-RGO/PANI composites are in a stacked layered structure of "PANI-(E-RGO)-PANI".The E-RGO and PANI are connected by covalent bond and strong ?-? conjugation,providing an improvement in structural stability.The electrochemical test results show that the electrochemical performance of E-RGO/PANI is improved compared with single component.The specific capacitance of E-RGO-10/PANI,E-RGO-12/PANI and E-RGO-15/PANI at 0.6 A/g are 385,398 and 364 F/g,respectively.The specific capacitance retention rate is 51.9%,64.8%and 46.2%.After the cycle stability test,the capacitance retention rate is 72.8%,77.8%and 71.4%.The specific capacitance and retention rate of E-RGO-12/PANI composite are the highest among the three composites.What's more,E-RGO-12/PANI exhibits smallest Rs and Rct,and the straight line is nearly parallel to the Z" axis,indicating that the composite has the best electrochemical performance.Through the characterization and performance analysis of different functionalized graphene/PANI composites,the reasons for the electrochemical performance improvement are summarized.The composites are in a layered structure with a rough surface.The PAN I network attaches on functionalized graphene sheet.The overall ?bond on the graphene surface forms a conjugate structure with the benzene ring in PANI chain.The electrostatic effect makes the PANI adhere to the graphene sheets.The functional groups on GO and reduced graphene oxide(RGO)can be used as active sites for the polymerization of aniline,so that the polymerization reaction mainly occurs on the graphene sheets,and graphene acts as substrate in composites.The amino groups introduced on the surface of FRGO and E-RGO can form a covalent bond with PANI to prevent PANI from falling off.Therefore,the existence of various binding forces between functionalized graphene and PAN I can confine PAN I on the graphene sheet and improve the structural stability.The carrier function of the graphene sheet can make up for the defects that PANI is easily susceptible structural damages in the redox process The hexadecyltrimethylammonium bromide(CTAB)used during the dispersion of GO and RGO can reduce the agglomeration of graphene,make it disperse in the aniline solution uniformly and increase the utilization rate of graphene.The presence of RGO can induce PANI to crystallize and improve crystallinity and conductivity.The improvement in electrochemical performance of composite originates from the stable structure,the synergistic effect between components and the joint contribution of electric double layer capacitance and pseudocapacitance.