MnO2 assisted oxidative polymerization of aniline on graphene sheets: Superior nanocomposite electrodes for electrochemical supercapacitors

Abstract

Graphene-polyaniline nanocomposite electrodes have been developed via oxidative polymerization of aniline by MnO₂ on a graphene surface for electrochemical supercapacitor applications. The formation mechanism of the above nanocomposite indicates that the MnO₂ undergoes oxidative disintegration and results in porous polyaniline (PANI) nanofibers formation on the graphene surface. The electron microscopic (SEM and TEM) images clearly showed the presence of porous PANI nanofiber formation on the graphene-PANI nanocomposites. The XRD, SEM-EDX and TG analysis confirmed the complete removal/degradation of MnO₂ during the oxidative polymerization of aniline. For comparison, graphene-PANI nanocomposites have also been prepared via conventional polymerization using (NH₄)₂S₂O₈ as oxidant in acidic medium and the effect of carbon nanotube (CNT) addition has been studied. The electrochemical properties of different graphene-PANI nanocomposites have been investigated using galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy measurements. A superior supercapacitive performance (∼15 to 40% more than the reported capacitance) has been observed for the graphene-PANI nanocomposite electrode obtained via oxidative polymerization of aniline by MnO_2. Addition of CNT into the graphene-PANI nanocomposite prepared via the conventional polymerization method showed improved specific capacitance and stability. Carbon nanofibers and graphite have been used as the carbon source and the effect of the carbon source on the specific capacitance has been investigated.