Electrochemical capacitive properties of synthesized nanostructured Manganese Oxides-Graphene composites

Abstract

The development of energy storage systems with regard to ever-increasing environmental as well as ecological concerns is undoubtedly one of the greatest challenges facing our modern society. Electrochemical capacitors are becoming attractive and efficient energy storage devices in this regard.

In this study, a total of seven materials viz. Mn3O4, MnO2, MnO2-Mn3O4 binary phase, Graphene (G), Mn3O4/G, MnO2/G and MnO2-Mn3O4/G have been successfully synthesized by a gel formation method under different conditions and their candidacy as electrochemical capacitor has been carried out. The chemical, elemental, structural, morphological and thermal characterization of the materials has also been carried out. The as-prepared materials were used to modify a graphite electrode by casting method. Electrochemical characterization for the determination of capacitance of the modified electrode were carried out using cyclic voltammetry and chronopotentiometry in 0.5 M Na2SO4 solution.

Among these synthesized materials, Mn3O4/G demonstrated the highest (442.4 F g-1) and MnO2-Mn3O4/G, the second highest (166.6 F g-1) specific capacitances values which are higher than graphene (127.6 F g-1). Mn3O4/G also shows the highest (22.1 W h kg−1) energy density values and MnO2-Mn3O4/G, the second highest (8.2 W h kg−1) which are also higher than graphene (6.4 W h kg−1). The prepared materials demonstrated the random distribution of power density values in which Mn3O4/G shows the highest (780.2 W kg−1) and MnO2-Mn3O4/G, the second highest (428.6 W kg−1) power density values which are also higher than graphene (150.1 W kg−1). The electrochemical performance of Mn3O4/G and MnO2-Mn3O4/G than that of graphene may be due to their highly conductive network, porous morphologies and synergy between the manganese oxides and graphene materials within the composite. This study on the synthesized materials indicates that Mn3O4/G and MnO2-Mn3O4/G have the great potential for application to practical energy storage devices, although further work should be carried out to upscale such compound without compromising the performance.

Key words: Manganese oxides, graphene, nanocomposites, electrochemical performance, supercapacitor applications.