The Fabrication And Performance Of Flexible Graphene/polyaniline Composite Film For Solid-state Supercapacitoes

With the development of wearable devices and flexible displays,more and more attentions have been paid to the preparation of flexible energy storage devices.Therefore,the preparation of flexible electrode materials with ultra-high flexibility and foldability is becoming a research hotspot.The porous graphene film material not only shows the advantages of graphene,including high electrical conductivity,good thermal stability,and good mechanical properties,but also shows some unique advantages,such as high specific surface area,ultra-high flexibility,and so forth.Therefore,the porous graphene film has a wide range of applications in electromagnetic shielding,flexible energy storage,sensors,and other fields.As a typical electrode material for supercapacitors,graphene poccesses the theoretical specific capacitance of 550 F/g,but the practical test value is lower than 220 F/g.Furthermore,as a kind of pure carbon material,graphene shows extremely strong hydrophobicity that goes against the electrochemical performance in aqueous electrolyte during the charging and discharging processes.Fortunately,these disadvantages can be overcome by physical or chemical modification or addition of pseudocapacitance materials.Polyaniline(PANI),as a traditional conductive polymer material,shows the advantages of cheap raw materials,simple process,and so on.Therefore,PANI has broad application and is widely favored by reseachers engaged in multiple fields.However,the molecular chain of PANI is rigid,and the solubility of PANI is extremely poor.Pure PANI is not conductive,but the conductivity of PANI can be improved by protonic acid doping,which increases the difficulty of processing and hinders its development in some fields.The theoretical specific capacitance of PANI is 770 F/g,demonstrating that PANI is an excellent supercapacitor electrode material.However,the electrochemical stability of PANI is extremely poor.Fortunately,this defect can be overcome by compounding PANI with carbon materials,such as graphene and manganese dioxide.At present,the flexibility of the porous graphene film materials is very limited,and most of the assembled solid flexible supercapacitors can only bend 150°.Herein,we prepared a graphene(RGO)porous film,which can be repeatedly folded to 180° and even double folded,by limited foaming during the process of chemical reduction of the graphene oxide film.In order to improve the performance of the electrode materials,we improved the hydrophilicity of the graphene film by introducing L-cysteine.Moreover,the capacitance of the electrode material is further increased by adding polyaniline.The detail works are as follows:1.We prepared the GO film by evaporating the solvent water at room temperature.Then,we prepared a porous RGO film,which can be multi-folded and even double-folded,by using hydrated hydrazine as the reducing agent and alumina ceramic chips as the jig.In order to improve the hydrophilicity of the electrode material,a certain proportion of L-cysteine was added to prepare a modified graphene(L-RGO)film material,and then the PANI was loaded on the surface of the porous films by anode electropolymerization(AEP).The capacitance of the L-RGO/PANI film electrode material is 270 F/g(0.5 A/g),which is larger than that of the pure porous graphene film electrode.2.We prepared the PANI-RGO composite films through chemical polymerization.Polyaniline grew in situ on graphene oxide sheets,and then PANI-GO composite films material were obtained by filtration.Through a limited expansion of reduction process,the porous PANI-RGO composite films were successfully prepared.The films can be single folded and double folded without obvious crease,showing good flexibility.The specific capacitance of the PANI-RGO composite film material is 680 F/g(0.5 A/g),but the specific capacitance of the pure RGO film is just 140 F/g(0.5 A/g).3.The foldable solid-state supercapacitor were assembled using the foldable electrode material prepared above,and the surface capacitance of the solid-state supercapacitor derived from PANI-RGO film is 227 mF/cm2(0.5 mA/cm2).