Electrochemical Supercapacitors Based On Graphene Composite Materials

As a unique electrochemical energy storage device, supercapacitorpossesses outstanding high-power output capability, stability and ultralongcycle life. Graphene, known as one-atom-thick two-dimensional conjugatedcarbon sheet, exhibits excellent conductivity, mechanical properties,electrochemical stability, huge theoretical specific surface area, variouschemical modifications and assembly behaviors, as well as low-cost chemicalsynthesis methods, etc. Therefore, graphene has been regarded as ahigh-performance supercapacitor electrode material promising for practicalapplications. This dissertation focuses on the synthesis and assembly ofcomposite materials based on chemically converted graphene and redox-activepseudo-capacitive materials. Two composite electrode materials includingchemically converted graphene/polyaniline nanofiber composite (G-PNF) filmand2-aminoanthraquinone modified self-assemble graphene hydrogel(AQSGH) were prepared, and their compositions, morphologies andelectrochemical performances were characterized. The main results aresummarized as follows.(1) With the assistance of ultrasonication, stable G-PNF composite waterdispersion was prepared by non-covalent electrostatic interactions. Layeredcomposite films with sandwich structure were obtained by filtration-inducedflow-directed assembly. Free-standing G-PNF composite film with44wt%grapheneshows good mechanical properties and flexibility, whose conductivity is10timeshigher than that of polyaniline nanofiber. The composite film shows specificcapacitance of210F/g (or160F/cm3) at0.3A/g charge/discharge current density.Compared to polyaniline nanofiber, supercapacitor based on G-PNF film showsobviously improved rate performance, cycle life and lower internal resistance,exhibiting the synergic effect of both components. (2) A redox-active small organic molecule,2-aminoanthraquinone, werecovalently modified on graphene oxide sheets. Macroporous AQSGHs withgood conductivity and mechanical properties were prepared by chemicalreduction induced self-assembly. As supercapacitor electrode, AQSGH showssingle-electrode specific capacitance of258F/g at charge/discharge currentdensity of0.3A/g, in which2-aminoanthraquinone moieties provided redoxpseudocapacitance of~65F/g. Ascribing to the macroporous, conductive andmechanical stable structure of graphene hydrogel substance, the redoxcapacitance of2-aminoanthraquinone was efficiently utilized. Therefore,AQSGH shows outstanding rate performance and excellent cycle life, and theadvantages of both components were adequately exhibited.