MnO2/graphene Nanocomposite Electrode Using for Supercapacitors

In the new century, energy storage has emerged to be one of the major topics, of various powersource devices, supercapacitors, also known as electrochemical capacitors (ECs), have raisedmuch attention in the field of applied electrochemical energy conservation/storage systems.Supercapacitors are electricity storage devices between conventional capacitors and rechargeablebatteries. They have a wide application in electric vehicles, portable electronic devices, memoryback-up devices, large industrial equipment [1]. By contrast with traditional capacitors,supercapacitors offer advantages of faster dynamics of charge–discharge, higher power andenergy density, longer cyclic life, and lower maintenance. In order to increase the energy densityof supercapacitors, electrode materials with higher active surface area and conductivity arerequired. Carbon nanomaterials, in particular as electrode materials for supercapacitors, haveattracted the attention of the scientific community in electrochemical double layer capacitors(EDLCs). As a typical carbon material, graphene, with sp2-hybridized carbon atoms packagedinto a honeycomb lattice structure, is identified as having great chemical and thermal stability,high mechanical flexibility, superior electrical conductivity, and large surface area. However, themaximum capacitance is limited by the active electrode surface area and can t meet therequirements for a capacitor [1]. Compared with one dimensional carbon materials, the uniqueplanar 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 aselectrode materials for pseudocapacitors. Among these oxides, MnO2, due to its high theoreticalspecific capacitance (1370), low cost, abundance, and environmentally friendly nature, hasdrawn tremendous attention as an active electrode material [1-3]. But the major challenge is toincrease the performance of the metal oxide that makes adding materials to it in order to achieve this goal. Therefore, we have investigated graphene nanosheets with its special feature. Grapheneoxide nanosheets were synthesized by using a Hummers method from graphite in ourexperiment. The graphene thin film will be deposited on the conductive substrate by thesuspension of graphene. Then, MnO2 nanostructures were electrodeposited from a mixture oftwo 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 electrochemicaldeposition process. The mass loading of MnO2 can be well controlled by adjusting the depositioncurrent and deposition time. The morphologies of the graphene–MnO2 nanocomposites wereexamined by scanning electron microscopy (SEM). FT-IR spectra of products in KBr pelletswere recorded. Power X-ray diffraction (XRD) patterns of samples were detected using a PhilipXRD X PERT PRO diffractometer with Cu Ka X-ray radiation. To test the electrochemicalproperties of the samples, a classical three-electrode cell was used electrochemical workstation.The electrochemical behaviors of the supercapacitor systems were estimated by cyclicvoltammograms (CV) and galvanostatic charge–discharge and electrochemical impedancespectroscopy (EIS). The synergistic effect between the high conductivity of graphene and pseudocapacitance of MnO2 generates large capacitance of composites. The GO/MnO2 compositeexhibits a considerable specific capacitance current density in 1 M Na2SO4 aqueous solution andgood long-term cycle stability.

Keywords:

Supercapacitor , Electrode , MnO2 , Graphene