Capacitive Properties Of Reduced Graphene Oxide/Polyaniline Composite Material With Different Deoxidization Degree

Supercapacitor, also called electrochemical capacitor or ultra-capacitor, is a type of energy storage device which fills the gap between typical dielectric capacitors and secondary battery. For the unique advantages, such as high power density, long cycle life, environmental friendliness, rapid charge/discharge and so on, supercapacitor has been widely exploited in the field of energy storage recently. The performance of supercapacitor is greatly influenced by the electrode material. Therefore, the effort to seek high conductivity and reversible electrode material has been a hot topic in the field. Polyaniline is a traditional electrode material, however, the bad cycle stability limits the practical application. Carbon materials possess unique properties and have been regarded as an functional component for making composite materials. Reduced graphene oxide (RGO), with few oxygen-containing functional groups of graphene oxide, the conductivity is partly restored, is a kind of promising electrode materials for supercapacitor.In this paper, modified Hummers method was employed to synthesize graphite oxide. Reduced graphene oxide (RGO) was obtained by ultrasonication of graphene oxide and then reduced by sodium borohydride. Finally, RGO/PANI composites were prepared by in situ polymerization. The surface morphology and functional groups of the composites were studied by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible absorption spectrum (UV-vis). Meanwhile, the specific capacitance, rate capability and cycle stability of the composite material were investigated using cyclic voltammetry.The results show that:(1) RGO/PANI composites were prepared by in-situ polymerization. Homogeneous PANI nanofibers have grown on RGO surface.(2) The specific capacitance of RGO/PANI composites increased firstly and then decreased with the improvement of RGO reduction degree. The low specific capacitance was obtained as the reduction degree was low, due to its low conductivity. When the reduction degree increased, the conductivity of RGO was improved as well as contained right amount of functional groups for dispersing PANI, which could effectively reduce the aggregation of PANI, enhance the kinetic for both charge transfer and ion transport throughout the electrode. Meanwhile it could provide the electrical double layer capacitance. When the reduction degree continued to improve, less functional groups resulted in longer chain and the aggregation of PANI.(3) Compared with PANI, the rate capability and cycle stability of RGO/PANI composites were improved due to RGO served as a elastic buffer to accommodate the volumetric change of the PANI chains.