Study On The Preparation And Electrochemical Performance Of Graphene-based Carbon Nanomaterials

Graphene, a single layer of carbon atoms with two-dimensional crystal structures,is a new member of the carbon family. Graphene has attracted great attention for itsoutstanding physical and chemical properties such as high specific surface area,conductivity, thermal stability and quantum tunnel effect. In the past decade, it hasbecome a research focus. The performance of carbon nanomaterial usually depends onits structure and morphology, which show great application potential in energy storage,catalysis, sensors and electronics, optics, etc. The main targets of this paper are asfollows:（1） Graphene is modified by physicochemical methods to obtaingraphene-based nanomaterials with more excellent performances;（2） the internalconnection of structures and electrochemical properties and the electrochemicalapplications （supercapacitors and lithium ion batteries） of graphene-basednanomaterials are systematically researched, which could lay the foundation ofpractical application of graphene nanomaterials. Main research contents are as follows:（1） High-quality graphene scrolls （GSS） are designed using a facile and novelmicroexplosion method under an ultrasonic reaction between MnO2and H2O2. Themethodology successfully realizes the transformation from2-dimensional （2D）material to nearly1D material. The scrolled mechanism is proposed and theircapacitance properties are investigated in this work. Compared with the specificcapacity of110F g^-1for graphene sheets, a remarkable capacity of162.2F g^-1isobtained at the current density of1.0A g^-1in6M KOH aqueous solution due to theirunique scrolled conformation, porous structure, open ends/edges and adjustableinterlayer distance. The capacity value is increased by about50%only because of thetopological change of graphene sheets. Meanwhile, GSS exhibit excellent long-termcycling stability along with96.8%retained after1000cycles at1.0A g^-1. All datassuggest that this study could offer an insightful approach for the preparation anddevelopment of GSS. These encouraging results indicate that GSS based on thetopological structure of graphene sheets are a kind of promising material forsupercapacitors.（2） Partial scrolled graphene are designed by a simple microexplosion techniqueusing a mild ionic catalyst-Fe³⁺, and assemble sroll-sheet conjoined nanomaterials（GS-GSS） based on graphene （GS） with unscrolled parts for enhanced supercapacitor properties. The morphology and structure of GS-GSS are characterized bytransmmision electron microscope, N2adsorption/desorption, Raman spectra andenergy dispersive spectrometer. The results demonstrate that the scrolled structurepresents on the edges of GS form GS-GSS and the scroll rate of nanomaterials is about30%. Electrochemical dates show that the specific capacitance of GS-GSS (224F g^-1at1.0A g^-1in1M H2SO4) is much higher than that of GS (137F g^-1) andGS-MWCNTs-7-3(121F g^-1), the capacity value is increased by about100%onlybecause of the difference of tubular structure （scroll has the open ends and edges,while the carbon nanotubes are closed）. Therefore, the GS-GSS are promisinggraphene-based materials for supercapacitors. What’s more, it is expected for GS-GSSnanomaterials to replace the traditional GS-MWCNTs nanocomposites for potentialapplications in future.（3） In this study, for increasing the utilization of closed pore volumes of carbonnanotubes （CNTs） in conventional graphene-CNTs composites, multi-wall fullerenenanopipes （MWFNs） are adopted to replace the pristine, nearly endless and highlytangled CNTs. The CNTs are tailored into MWFNs with10-300nm lengths and openends, and a nanocomposite film of well-dispersed MWFNs as macromolecules ongraphene （GS） is prepared by a facile wet-chemical route. The morphology of theresulting materials is characterized by scanning electron microscope （SEM） and theirelectrochemical activities are investigated, suggesting that the MWFNs asmacromolecules could uniformly modify and distribute on the surface of graphene andform a film structure with graphene. The introduction of MWFNs could effectivelyenhance the utilization of closed pore volumes of nanopipes, inhibit the stacking ofgraphene and facilitate the transportation of the electrolyte ion and electron in theelectrode. Such the GS/MWFNs nanocomposites obtain ultrahigh electrochemicalactivities. These results indicate that the unique MWFNs would stimulate thedevelopment of several energy-efficient technologies.（4） An ordered mesoporous carbon （OMC） with controllable molecule crystal andplatelet graphitic pore walls, which is directionally grown on the internal pore walls ofSBA^-15or anchors at liquid/silica interfaces by molecule engineering, has beeninvestigated as lithium ion anodes. It is found that the OMC exhibits high kinetics, rateand cycling performance. The i0and DLiare almost constant after50cycles. OMCshows a high reversible specific capacity of153.9mAh g^-1at the current density ashigh as3500mA g^-1. The excellent electrochemical performance could be attributed tothe presence of the porosity and platelet graphitic pore walls. （5） Mesoporous carbons （MCs） with nanosheet-like walls have been prepared aselectrodes for lithium-ion batteries by a simple one-step infiltrating method under theaction of capillary flow. The influence of heat treatment temperature on the surfacetopography, pore/phase structure and anode performances of as-prepared materials hasbeen investigated. The results reveal that melted liquid-crystal polycyclic aromatichydrocarbons could be anchored on liquid/silica interfaces by molecule engineering.After carbonization, the nanosheets are formed as the pore walls of MCs and areperpendicular to the long axis of pores. The anode properties demonstrate that C^-1200displays higher reversible capacitance than those treated in higher temperature. Therate performances of C^-1200and C^-1800are similar and more excellent than that ofC-2400. These improved lithium ion anode properties could be attributed to thenanosheet-like walls of MCs which can be influenced by the heat treatmenttemperature.