Innovative approach for the synthesis of graphene/MnO2 nanocomposites and their electrochemical behavior

Abstract

Graphene-manganese dioxide composites were prepared using a simple one step method consisting of the electrochemical exfoliation of graphite in the presence of KMnO4 in 0.1 м H2SO4 at low temperature. In these conditions, the freshly exfoliated graphene sheets (EG) spontaneously reduce the permanganate ions and EG sheets decorated with MnO2 nanoparticles are obtained. This was confirmed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Raman, and X-ray photoelectron spectroscopies and thermogravimetric analysis. The electrochemical properties of EG@MnO2 material were investigated and discussed. Electrodes based on the composite material exhibited enhanced capacitive performances compared to those made from pure graphene sheets. This was attributed to the synergic effect between the two components (graphene sheets and manganese dioxide nanoparticles) and to a larger porosity of the EG@MnO2 electrode compared to the EG electrode. Additionally, over 91.6% of original capacitance was retained after 4000 cycles, indicating a very good cycling capability of the composite material. Remarkably, the composite electrode showed promising properties in aqueous medium by exhibiting a large and stable operating voltage up 2 V. The results presented in this article could serve as a guide for improving the energy density of supercapacitors in aqueous media.