Study On The Electrochemical Performance Of Graphene Composites As Supercapacitor Electrode Materials

A super-capacitor is a new kind of energy storage device, whose performance is situatedbetween the traditional capacitor and the electro-chemical cell with much larger capacity thanconventional physical capacitors, and higher rate capability than electro-chemical batteries.Supercapacitors are environmentally friendly, of high safety, and can be operated in a widetemperature range，with a long cycling life. Thus, supercapacitors show great potentialapplications in communication, transportation, electronics, and aviation. Electrode materialsas a key factor to determine the performance of super-capacitor is the the current researchfocus. To date, carbon materials, transitionmetal oxides and conducting polymers have beenidentified as most promising materials for SCs.Graphene is a new carbon material composing of closely packed single layer carbonatoms, because of special nano-structure and excellent performance, which has shown greatpotential application in electronic, optics, magnetism, catalysis, sensors, energy storage andother areas. Recently, one new perspective is to utilize this ideal single-atom-thick GNS as asupport to anchor functional nanomaterials to form new nanocomposites with potentialapplication in catalysis, light energy conversion.In this paper, firstly, graphite oxide was prepared from natural graphite by a modifiedHummers method, then, glucose was used as reducing agent to prepare the GNS. Finally, theprepared GNS dispersion was used as substrate to prepare GNS composite electrode materialsby the method of in situ growth/polymerization, at the same time the microstructure andelectrochemical performance were also investigated. The main work and innovation of thethesis are listed as following:A green and facile approach was demonstrated to prepare graphene nanosheets/ZnO(GNS/ZnO) composites for supercapacitor materials. First glucose instead of highly toxichydrazine as a reducing agent was used to reduce as-obtained GO to GNS. With this method,the prepared GNS was well dispersed in aqueous solution. Then, in the GNS dispersion, ZnOwas directly grown onto conducting graphene nanosheets by in situ method to obtainGNS/ZnO composites. The small ZnO particles homogeneously anchor onto graphene sheetskeeping the neighboring sheets separate. The electrochemical performances of theseelectrodes were analyzed by cyclic voltammetry, electrochemical impedance spectrometryand chronopotentiometry. Results showed that the GNS/ZnO composites displayed superiorcapacitive performance with large capacitance (62.2F/g), excellent cyclicperformance, and maximum power density (8.1kW/kg) as compared with pure grapheneelectrodes.GNS as substrate, we prepared GNS/LDH composite for supercapacitor material hasbeen fabricated by a hydrothermal method. Scanning electron microscopy and transmissionelectron microscopy results reveal that Ni/Al LDH platelets homogeneously grew onto thesurfaces of the GNSs. The composite exhibits a maximum specific capacitance of781.5F/gand excellent cycle life with an increase of the specific capacitance of38.07%after50cycletests. Even after200cycle tests, the increase of the capacitance is22.56%compared with theinitial capacitance.A hybrid reduced graphene nanosheet/Polyaniline (GNS/PANI) composite forsupercapacitor material has been fabricated by an in situ polymerization method. Scanningelectron microscopy (SEM) and transmission electron microscopy (TEM) results reveal thatPANI nano-wafers (50nm) homogeneously grew onto the surfaces of GNSs。The locatedPANI nano-wafers one hand keep the neighboring sheets separate, the other hand improve thespecific capacitance of the composites.The composite exhibits a maximum specificcapacitance of329.5F/g and excellent cycle life.