MnO2/graphene Nanocomposite Electrode Using for Supercapacitors

In the new century, energy storage has emerged to be one of the major topics, of various power source devices, supercapacitors, also known as electrochemical capacitors (ECs), have raised much attention in the field of applied electrochemical energy conservation/storage systems. Supercapacitors are electricity storage devices between conventional capacitors and rechargeable batteries. They have a wide application in electric vehicles, portable electronic devices, memory back-up devices, large industrial equipment [1]. By contrast with traditional capacitors, supercapacitors offer advantages of faster dynamics of charge–discharge, higher power and energy density, longer cyclic life, and lower maintenance. In order to increase the energy density of supercapacitors, electrode materials with higher active surface area and conductivity are required. Carbon nanomaterials, in particular as electrode materials for supercapacitors, have attracted the attention of the scientific community in electrochemical double layer capacitors (EDLCs). As a typical carbon material, graphene, with sp2-hybridized carbon atoms packaged into a honeycomb lattice structure, is identified as having great chemical and thermal stability, high mechanical flexibility, superior electrical conductivity, and large surface area. However, the maximum capacitance is limited by the active electrode surface area and can t meet the requirements for a capacitor [1]. Compared with one dimensional carbon materials, the unique planar structure of graphene makes it easier and more flexible to integrate with metal oxides. Various noble and transition metal oxides such as MnO2, RuO2, NiO, and SnO2 were used as electrode materials for pseudocapacitors. Among these oxides, MnO2, due to its high theoretical specific capacitance (1370 𝐹𝑔−1), low cost, abundance, and environmentally friendly nature, has drawn tremendous attention as an active electrode material [1-3]. But the major challenge is to increase the performance of the metal oxide that makes adding materials to it in order to achieve 308 this goal. Therefore, we have investigated graphene nanosheets with its special feature. Graphene oxide nanosheets were synthesized by using a Hummers method from graphite in our experiment. The graphene thin film will be deposited on the conductive substrate by the suspension of graphene. Then, MnO2 nanostructures were electrodeposited from a mixture of two different types of solutions (0.1 M Na2SO4 and 0.1 Mn(CH3COO)2) onto the graphene film. We have deposited nanostructured MnO2 materials on graphene through an electrochemical deposition process. The mass loading of MnO2 can be well controlled by adjusting the deposition current and deposition time. The morphologies of the graphene–MnO2 nanocomposites were examined by scanning electron microscopy (SEM). FT-IR spectra of products in KBr pellets were recorded. Power X-ray diffraction (XRD) patterns of samples were detected using a Philip XRD X PERT PRO diffractometer with Cu Ka X-ray radiation. To test the electrochemical properties of the samples, a classical three-electrode cell was used electrochemical workstation. The electrochemical behaviors of the supercapacitor systems were estimated by cyclic voltammograms (CV) and galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The synergistic effect between the high conductivity of graphene and pseudo capacitance of MnO2 generates large capacitance of composites. The GO/MnO2 composite exhibits a considerable specific capacitance current density in 1 M Na2SO4 aqueous solution and good long-term cycle stability.