The Preparation Of Carbon-based Materials And Their Application In The Field Of Supercapacitors And Microwave Absorption

In modern society people pay more attention to supercapacitor and microwave absorption,where materials play the key role in these applications.Recently,carbon materials have been widely used in many fields such as machinery,electronics,aviation and chemical industry due to their advantages of diverse sources and stable structure.Nevertheless,the poor inherent capacitance and single microwave absorption mechanism of carbon materials have been the bottleneck for their applications.In this paper,aiming to solve these above problems,we adopted composite and modification methods to prepare a variety of new high-performance carbon-based materials,and explored their application potential in supercapacitors and microwave absorption.The fast development of portable devices has greatly stimulated the demand for flexible supercapacitors?FSCs?.The key to assembling FSCs lies in the development of electrodes with high performance and good flexibility.One-dimensional?1D?carbon fiber has attracted extensive attention due to its high conductivity and flexibility.In this work,oxygeneous groups modified nitrogen-doped carbon fibers cloth?ONCC?was obtained through annealing the pre-oxidized polyacrylonitrile cloth?PPC?,followed by a facile oxidation process using a mixture of concentrated sulfuric acid and concentrated nitric acid.By changing annealing temperature,the nitrogen content can be controlled in the obtained ONCC.It was found that the PPC annealed at 950oC followed by acid etching for 60 min could deliver the excellent areal and gravimetric specific capacitance of 1385 mF cm^-2 and 294.7 F g^-11 at the current density of 1 mA cm^-2,outstanding rate performance and superb cycling stability.Furthermore,the assembled FSC delivered a high energy density of 19.8?Wh cm^-2(4.03 Wh kg^-1)at a power density of 50.1?W cm^-2(10.2 W kg^-1)and good flexibility under different bending conditions.Graphene,as a popular two-dimensional carbon based material,has been widely integrated with cobalt nickel sulfide nanomaterials for high-capacitance supercapacitors.However,the limited capacity and poor adhesion strength between graphene and cobalt nickel sulfide could reasult in the unsatisfactory capacitance and stability performance.In order to deal with the above issues,we used phytic acid,the biological small molecules,to promote the nucleation of nickel and cobalt ions on the graphene oxide.After hydrothermal sulfidation,cobalt nickel sulfide nanoparticles/phosphate functional group-modified reduction oxidation graphene composites?NiCo₂S₄/PRGO?were successfully synthesized.In this experiment,the electrochemical properties of NiCo₂S₄/PRGO as the supercapacitor electrode material were studied and the effects about different amounts of phytic acid on the morphology and properties of the composite were further investigated.The final results showed that the addition of phytic acid could enhance the binding force between NiCo₂S₄ and graphene,so as to obtain high contact area of electrode material/electrolyte,good infiltration of electrolyte and finally excellent electrochemical properties of the material.Besides the promising applications in energy storage,graphene-based materials have also been widely studied in electromagnetic shielding and absorption in recent years.However,their single dielectric loss and non-magnetic properties can hardly meet the requirements of strong absorption and broadband of microwave absorbers.Porous?1-2.5?m?graphene was successfully prepared via a simple pyrolysis process and the minimum reflection loss?RL?value reached-48 dB at 9.8 GHz after the structure modification,which demonstrated that porous graphene?PG?possesses outstanding MA performance than the ordinary graphene?OG?.In order to strengthen the magnetic loss and boost the impedance matching,Fe₃O₄ nanoparticles?¹0 nm?were subsequently deposited uniformly on the surface of PG via in situ precipitation.It was found that the as-prepared porous graphene-Fe₃O₄?PG-Fe₃O₄?composites showed very high MA performance and the minimum RL of-53.0 dB could achieve at 5.4 GHz with the thickness of 6.1 mm.The absorption bandwidth of RL less than-10 dB was from 12.6 to 18.0 GHz?5.4 GHz?with a thin thickness of 2.7 mm.The excellent MA properties of PG-Fe₃O₄ composites were the consequence of the perfect impedance matching,porous structure as well as the multi-polarization.