Construction And Supercapacitive Performance Of Carbon Nanotube-graphene Heterostructure Carbon Structure And Its Composites

The use and development of the clean energy make its storage more and moreimportant, and so it is urgent to develop an effective energy storage device.Supercapacitor is a new kind of energy storage device whose high power density andexcellent cycle life are intrested by researchers. In the last ten years, carbon nanotubes(CNTs) were used as typical double layer supercapacitor electrode materials becauseof their good mechanical properties, chemical stability and conductivity. CNTs withmicron length, especially, multi-walled carbon nanotubes (MWCNTs) are easy to betwingled to “ropes”, and the enclosed structure of the carbon nanotubes ends makesthe electrolyte ions can not reach the inner wall carbon nanotubes. To improve theirelectrochemical performance, it is necessary that the researchers unzip, dope andmodify MWCNTs by compositing.In this paper, we use a modified Hummers’ method to cut MWCNTs to getcarbon nanotube-graphene oxide heterogeneous structure (CNTGO), and thennitrogen-doped carbon nanotube reduced graphene oixde heterogeneous carboncomposites (N-CNTRGO) and NiO/CNTRGO composites with high-performancewere prepared by using the resultant CNTGO. The appropriate analytical method andtechnique are used to characterize the morphology, structure and conponents of theresultant materials. Moreover, the electrochemical performances of the as-preparedsamples are investigated in details. The main contents are following:We unzipped MWCNTs to form Water-dispersed CNTGO via modifiedHummers’ method. Furtherore, we obtained CNTRGO by following thermaltreatment of CNTGO. The results showed that the CNTGO was composed of the shortcarbon nanotubes and the multi-layer graphene formed by unzipping MWCNTs, andalso the amount of the oxidizing agent affected the electrchemical properties ofCNTRGO. When the mass ratio of KMnO4to MWCNTs was up to4:1, CNTRGOelectrode material had a maximum specific capacitance of157and183F g-1at aspecific current of1A g-1in1mol L-1H2SO4and1mol L-1KOH respectively, whichwas9times than that of pure multi-walled carbon nanotubes in the same experimentalconditions. Furthermore, aftering3000charge/discharge cycles, the capacitance ofCNTRGO remains100%and82.5%of the initial value at a specific current of1A g-1in1mol L-1H2SO4and1mol L-1KOH respectively. The CNTRGO displays thepotential commercial potential for high performance energy storge devices.The N-CNTRGO was successfully synthesized by a facile hydrothermal method,in which hydrazine were used as the reducing agent(reduce CNTGO to CNTRGO)and nitrogen resource and aqueous ammonia(pH=10) were used as solvent. Theexperimental results indicated that the hydrothermal temperature play an importantrole in their structure, nitrogen content and electrochemical properties. When thehydrothermal temperature keeps at120°C, nitrogen content of N-CNTRGO materialis up to3.48%, at the same time, the sample exhibited the highest specificcapacitance (269.1F g1at1A g1). The electrode material had excellent cyclestability with the capacitance retention rate81%after5000cycles.NiO/CNTRGO composites were successfully synthesized by a facilesolvothermal method following thermal treatments. In the composite, CNTRGO isused as a substrate to support nickel oxide while NiO can effectively prevent theagglomeration of CNTRGO in the same time. When the NiO/CNTRGO compositewith mass of NiO to CNTRGO up to77.5%was used as an electrode, it exhibitedexcellent electrochemical performance. The specific capacitance of1010F g-1wasachieved at a specific current of1A g-1. In addition, after3000charge-dischargecycles, the capacitance of NiO/CNTRGO remains68%of the initial value at aspecific current of1A g-1.