Study On The Synthesis,Structure Andsupercapacitor Properties Of Liquid-like Nanofluids/Graphene Aerogel

Graphene is a kind of two-dimensional?2D?single sheet of sp² hybridized carbon atoms with unique structure properties such as an extraordinarily high electrical conductivity,high surface area?over 2600 m²/g?,low density,outstanding mechanical property and electrochemical stability.Graphene possess high specific capacitance when used as electrode material for supercapacitor.However,the 2D graphene nanosheets are very easy to reunite and re-form graphite structure,which has restricted achieving the true capacitance of graphene when used as supercapacitor electrode.Three-dimensional?3D?graphene aerogel with large surface area,extremely low density and abundant interconnected porous structures been developed to solve the restacking problem of graphene sheets,which have been used for high performance supercapacitor electrodes.Solvent-free nanofluid is a kind nano-material with long organic branched chains,which can possess liquid-like behavior without any solvents.Solvent-free nanofluid materials have wide potential as supercapacitor electrode material.In this work,we used carbon nanotube nanofluid?CNTF?,self-suspended polyaniline?S-PANI?and self-suspended polypyrrole?S-PPy?and graphene oxide?GO?as precursors,respectively,to obtain solvent-freenanofluidmaterial/graphenecompositeaerogelsvia hydrothermal/freeze-drying approach.We studied the structure and electrochemical performance of the as-prepared aerogels,the details are as follows:?1?We synthesized solvent-free CNTs nanofluids?CNTF?via ion-exchange method.Then we dissolved the as-prepared CNTF into GO aqueous solution and fabricated 3D-CNTF/RGO aerogel through hydrothermal reaction of the hybrid aqueous solution followed by free-drying.Our method has achieved the one-step self-assambly of 3D-CNTs/graphene materials.The lowest density of the as-obtained CNTF/RGO aerogel is 14.4 mg/cm³,very close to ultralight materials?10 mg/cm³?.The results of Scanning electron microscope?SEM?,Raman spectrum,X-ray diffraction?XRD?and transmission electron microscopy?TEM?tests showed that CNTF/RGO aerogel possess well organized 3D graphene frameworks.The N₂adsorbtion/desorption result showed that CNTF/RGO aerogel has hierarchical porous structure with 246.2 m²/g specific surface aera and 0.47 cm³/g porous volume.Significantly,when used as supercapacitor electrodes,a high specific capacity of421.8 F/g was acquired at 1 A/g and it still remained 136.5 F/g at 10 A/g.The capacitance has remained 71.4%after 10000 cycles.?2?Liquid paraffin microcapsules?LPMs?were synthesized via emulsion polymerization.CNTF/LPMs/RGO aerogel was obtained by hydrothermal/freeze-drying treatment of the mixed LPMS,CNTF and GO aqueous solution.Then,CNTF/LPMs/RGO aerogel and CNTF/RGO aerogel was carbonized in Ar₂atmosphere,and obtained carbonized CNTF/LPMs/RGO?CCLG?aerogel and carbonized CNTF/RGO?CCNG?aerogel.SEM,Raman spectrum and XRD text showed that LPMs and the organic layer around CNTF were successfully carbonized,forming a continuous carbon structure.Such carbonized structures could connect adjacent CNTs and graphene.According to the electrochemistry test,the cycling stability of the carbonized aerogel can reach 90%,however,the specific capacitance of the material has decreased compared to the un-carbonized material.?3?Solvent-free polyaniline?PANI?nanofluid was synthesized using a long-chain protonic acid containing a polyethylene glycol segment?NPES?as the dopant during the polymerization of aniline monomers.S-PANI/RGO aerogel was fabricated using S-PANI and GO hybrid aqueous solution as the precursor via a direct self-assembly method.FTIR,XPS and SEM confirm that S-PANI is cross-linked with GO sheets by hydrogen-bonding and?-?interactions,acting as separator between graphene sheets as well as connect the neighboring graphene sheets,thus preventing the restack of graphene sheets and support the 3D porous framework.The as prepared RGO/S-PANI aerogel exhibit high specific surface area of 335 m²/g and abundant porous volume of 0.61 cm³/g.When used as supercapacitor electrode,a high specific capacitance of 480 F/g at current density of 1 A/g was obtained,and it remained 334 F/g even at a high discharge rate of 40 A/g.An excellent long-term stability,with 96.14%of the initial capacitance remaining after10000 charging/discharging cycles at a rate of 10 A/g,was also achieved.The rate and cycling stability is among the best of the similar works.?4?The solvent-free PPy nanofluid?S-PPy?was prepared using NPES as the dopant during the polymerization of pyrrole monomers.Then S-PPy/RGO aerogel was prepared by hydrothermal/freeze-drying reaction of S-PPy and GO hybrid aqueous solution.The synthesis of S-PPy/RGO aerogel confirms that solvent-free nanofluid materials are universl precursors in preparing 3D graphene composite aerogels.The S-PPy/RGO aerogel electrode process excellent reversible charge-discharge ability,the highest specific capacity reached 800.9 F/g at the current density of 0.5 A/g,significantly,it remains 315 F/g at 40 A/g.Moreover,we found that the specific capacitance of S-PPy/RGO electrode could maintain 96.9after charge/discharge for 10000 times.Such excellent electrochemical performance may be attributed to the following reasons:Firstly,the anionic dopant NPES can suppresses the counterion drain effect of PPy during charge-discharge cycling.Secondly the flexible RGO nanosheets could accommodate large volumetric deformation of PPy molecules,thus preventing the structural pulverization of PPy chains.Thirdly,the 3D porous structured graphene networks can enhance the performance of the double layer effect.