Synthesis Of Graphene Films And Graphene-based Composites For Supercapacitor Application

Graphene is a new type of carbon material with2D cellular lattice structure tightly piledup by single-layer carbon atoms. Because of its unique composition and structure, graphenepossesses of unusual mechanical, thermal and electrical properties and has potentialapplications in various fields such as mechanism, electronic technology. In this thesis,graphene films, graphene/polyacrylate sodium films and graphene/Mn₃O₄composites havebeen successfully synthesized using graphene oxide （GO） as the resources which produced bymodified Hummers method. Such materials are characterized by XRD, Raman, UV-vis, IR,TEM and TGA etc. The obtained graphene-based materials are used as electrode materials ofsupercapacitors and their capacitive behavior is measured by the consecutive galvanostaticcharge-discharge and cycling voltammetry. Main study results are summaried as follows:1. KI reducing method is used to reduce GO films into flexible graphene films withoutdestroying their integrity. The results shows that both the concentration of HCl and reactiontime in the system have great effect on the reduction of GO films. It is found that thegraphene films with good flexibility can be obtained in1mol L^-1HCl and50%KI for30min.When used as the electrode of supercapacitors, the specific capacitance of the graphene filmscan reach up to181F g^-1, and capacitance retention of approximately90%is obtained after600cycles in6mol L^-1KOH electrolyte solution,2. The graphene/polyacrylate sodium films with tailored pore size have been producedusing soluble graphene and polyacrylate sodium as the resources through vacuum filtration.The result demonstrates that the presence of polyacrylate sodium with the property ofmoisture-absorption can help to tune the pore sizes of graphene films between wet and dryconditions. Besides, the ratio of graphene and polyacrylate sodium has great influence on thepore size and property of the obtained films. The graphene/polyacrylate sodium films showgood capacitive property when used as the anode material in6mol L^-1KOH electrolytesolutions. The wet films have a specific capacitance of294.2F g^-1with the mass ratio ofgraphene and polyacrylate sodium fixed as10:1, while it also remains256.2F g^-1after dryingtreatment. Furthermore, its capacitance retention is about91%during the1000continuouscycles, which shows stable capacitive characters of the films. 3. A green method for synthesis of graphene/Mn₃O₄composites has been introduced.Both manganese salt and GO produced from modified Hummers method have been utilizedwith high efficiency, which are converted into rGO/Mn₃O₄composite by means of thermaldeoxygenation. The content of Mn₃O₄in rGO/Mn₃O₄composites can be tailored via varyingthe volume of supernatant liquid of pristine GO/MnSO₄suspension. This approach is verysimple without the fussy procedure for the separation of GO from the suspension, and thelarge amount of MnSO₄is reused as the sources. The maximum specific capacitance of theas-prepared rGO/Mn₃O₄composite is measured to be284F g^-1at50mA g^-1when employedas the anode material in saturated K₂SO₄electrolyte solutions.