Síntese e caracterização de Óxido de ferro e do compósito Óxido de ferro/Óxido de grafeno reduzido para aplicação em supercapacitores

Abstract

Electrochemical capacitors are energy storage devices that have high power density and higher energy density than a conventional capacitor, they are used in portable devices like cell phones and cameras. The materials used in these devices are carbon, conductive polymers and transition metal oxides. Currently, Fe2O3 is gaining prominence due to its low cost, non-toxicity, and easy handling. Composite metal oxides and carbonaceous materials have been extensively studied, because of the properties of these two materials, forming a hybrid supercapacitor. Among the carbonaceous materials, graphene gets prominence mainly because of the electrical conductivity, surface area and chemical stability. In this work, the Fe2O3 was synthesized by the polymeric precursor method and the graphene oxide was synthesized by the Hummers method. Physical characterization of Fe2O3 was performed by studying the calcination temperature effect on the structure and morphology of the oxide obtained by the polymeric precursors method which showed thermal transition between the γ - Fe2O3 and α - Fe2O3 phases that occurs between 370 and 600 ⁰C. The electrochemical characterization was performed by cycle voltammetry and galvanostatic charge/discharge. The cycle voltammetry showed pseudocapacitor behavior of Fe2O3. The specific capacitance values were calculated for charge/discharge and showed that the oxide calcined at 400 ⁰C obtained the highest value. The physical characterization of the reduced graphene oxide obtained was conducted to demonstrate the oxidation of the graphite and reducing the graphene oxide. Then the Fe2O3/rGO composite was synthesized and held their physical characterization, showing the synergistic effect of the two materials together. The cyclic voltammetry curves show that the composite exhibits a hybrid supercapacitor behavior, joining the pseudocapacitor characteristics of Fe2O3 with the graphene characteristics of electrochemical double layer capacitor. The specific capacitance values were calculated for charge/discharge and show that pure Fe2O3 obtained value greater than the composite synthesized in this work. Among the composites, which contained 80% Fe2O3 and 20% rGO had the highest specific capacitance.