Rereach On Preparation And Performance Of Modified Graphene-based Composite Electrodes For Supercapacitors

As an energy storage device,asymmetrical supercapacitors?ASCs?have attracted more and more scientific and commercial interests.And the key to obtain excellent electrochemical performances of ASCs is to develop electrode materials with large specific surface area,appropriate pore distribution and good wettability,forming large-area electric double layer between electrode materials and electrolyte,and improving the performance of supercapacitors.Graphene has many advantages such as large specific surface area,high conductivity,good mechanical property and excellent chemical stability,and holds promise as an ideal carrier material for composite electrodes in supercapacitors.At present,there are many methods to prepare graphene.Meanwhile,solution-based reduction of GO is the most promissing method owing to be suitable for large-scale industrial production and low requirements for equipments.However,it will agglomerate severely in aqueous solution because of the strong interaction between graphene sheets,and the inherent advantages of large specific surface area and high conductivity are lost,which will directly affect the electrochemical performances of electrode materials.Therefore,we need to improve the dispersity of graphene greatly,solving the problem of agglomeration,and making graphene dispersed well in aqueous solution.Furthermore,graphene is served as the carrier material to acquire electrode materials with excellent electrochemical performances.Firstly,we prepared naphthalene series nonionic surfactant?NSNS?using polyethylene glycol monomethyl ether?MPEG?,paratoluensulfonyl chloride?TsCl?and 2-naphthol.Then we discussed the influence of NSNS on the dispersity,specific surface area and conductivity of graphene.We found that the specific surface area of modified graphene is almost five times greater than that of graphene without modification.Meanwhile,the conductivity of modified graphene increased by 7-10times as much.Secondly,MnFe₂O₄ nanoparticles and modified graphene-MnFe₂O₄?NGM?binary composite were prepared.Observed by SEM,MnFe₂O₄ nanoparticles distributed uniformly on the surface graphene layers,and the sizes of which are almost only 20-30 nm.Furthermore,we change the additive amount of MnFe₂O₄nanoparticles and the influence of which on the electrochemical performances of binary composite electrodes were discussed.We find that NGM-5 has the largest capacitance of 321.2 F/g at the scanning rate of 20 mV/s,and the value is almost three times greater than NG.Finally,we use in situ chemical oxidative polymerization to prepare the ternary composite of NGM-5 wrapped PANI which is named NGMP.Furthermore,we change the additive amount of PANI and the influence of which on the electrochemical performances of ternary composite electrodes were discussed.We demonstrate that the optimal specific capacitance of ternary composite electrode is15-20 times greater than the pristine MnFe₂O₄.And NGMP-5 has the largest capacitance of 411.0 F/g,meanwhile,NGMP-5 has great cycling stability with a retention of 92.4%after 2000 cycles at 5 A/g.The excellent electrochemical performance of the ternary composite is due to the reasons as follows:first of all,successful interaction between NSNS and the surface of graphene leads to good dispersion of graphene;secondly,as carrier material,NG provides sufficient contact between MnFe₂O₄ nanoparticles and PANI,guaranteeing the fast and effective delivery of charges on electrodes;In addition,MnFe₂O₄nanoparticles can provide much more active sites in charge-discharge process,and the existence of a moderate amount of PANI can improve the electrical conductivity of composite materials,accelerating the transfer rate of electrons on composites'surface.