Fabrication of graphene/polypyrrole nanotube/MnO₂ nanotube composite and its supercapacitor application

A novel composite is fabricated through hybridizing graphene with polypyrrole (PPY) nanotube and manganese dioxide (MnO₂) nanotube to comprehensively utilize the electrical double layer capacitance and pseudo-capacitance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy are employed to characterize its structure. The SEM and TEM images illustrate that graphene/PPY nanotube/MnO ₂ nanotube composite (GPM) presents interconnected structure. The result of Raman analysis demonstrates the intimate interactions among PPY, graphene and MnO₂. In addition, cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) techniques are used to measure the electrochemical properties. It is revealed that GPM presents excellent high-rate performance and its capacitance is as high as 469.5 Fg^-1 at a current density of 0.3 Ag^-1, higher than that of PPY and chemically reduced graphene sheet as well as the materials reported in the literature. Furthermore, long-term charge-discharge cycle test confirms that the fabrication of GPM can effectively merge the merits of graphene, PPY and MnO₂. Additionally, EIS analysis illustrates that the presence of conductive graphene as well as the intimate interactions among graphene, PPY and MnO₂ lead to the good electrochemical stability.