Investigation Of Manganese Oxides-based Nanostructures For Supercapacitors

Energy is always an important issue for human beings.The ever-increasing population and economic development,raised the depletion of fossil fuels,resulting in massive emissions of greenhouse gases,climate changes,which create environmental problems.Fossil fuels,which are the main energy sources of the current world,are running low and alternative ways of generating and storing different types of energies are becoming daunting missions.Reviewable energy is very attractive because the source of the energy is often free and also environmental friendly.The key issues to utilize the renewable energies in a sustainable manner is how efficiently store the energies and provide them on demand.Therefore,the significance of the energy storage devices has been recognized in the recent time.With the development of portable electronics,flexible electronics has attracted tremendous interests.Many efforts have been made to fabricate flexible devices,such as laptops,tablets,smart-phones,foldable displays,artificial electronic skin,bendable transistors,e-papers,and military devices.All of these electronics require flexible,lightweight,and highly efficient energy storage technology.Conventional energy storage devices,such as batteries,have restrictions such as relatively low power,and long charging time.Electrochemical capacitors(ECs)also known as supercapacitors attracted significant attention due to their unique characteristics of high power density,long lifetime and excellent rate capability.To fulfil the requirements of next-generation electronic devices which demand the thin,lightweight and flexible electrodes with higher energy and power densities.The objective of this research was to synthesize different kind manganese oxides nanostructures,such as nanoparticles,nanorods,nanowires,nanosheets and to develop highly efficient electrode materials for supercapacitors applications.A simple one-step hydrothermal method is used to fabricate flexible electrode for supercapacitors without using any surfactant.Most attention had focused on MnO2,Cu0.45Mn0.55O2,Mn3O4 and rGO-Mn3O4 as a flexible electrode for pseudo-capacitor to enhance their energy storage characteristics.MnO2 has been selected due to the low cost of the raw material and environmental friendliness than any other transition metal oxide system.MnO2 can be controlled by synthesized under optimum conditions display high capacitance and exhibit good cycle profile.The synthesized samples have been characterized by multiple techniques,including the field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),high-resolution transmission electron microscopy(HRTEM),with energy dispersive X-ray spectroscopy(EDX),selected area electron diffraction(SAED),X-ray diffraction(XRD),x-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy(RS)and CHI 660D electrochemical workstation.Carbon textile(CT)is used as a substrate to investigate the electrochemical performance of active materials due to the unique characteristics of CT,such as high conductivity,flexibility,and chemical stability and cost-effective.CT has been used as a flexible conducting substrate in the study of flexible electrodes,it shows outstanding performance due to its high conductivity,excellent mechanical flexibility,strength,and lightweight architecture.The three-dimensional(3 D)porous structure with a rough texture which is highly favourable for the direct growth of active materials with high mass loading densities.We obtained some novel results for the supercapacitors flexible electrodes.3D MnO2 nanorod forest(NRF)network was grown on carbon textile(MnO2-NRF@CT)with the hierarchical porous structure as a binder-free electrode material for supercapacitor.Although binders is a necessary additive in the traditional slurry-casting method during the fabrication of electrodes,it decreases the electrical conductivity,prevents the access of ions to the surface of active materials,and increases the polarization of active materials due to their insulating and electrochemically inactive properties.Carbon textile based binder-free electrodes have unique merits over slurry-casting method,it can provide a large number of electrochemically active sites,higher surface area to volume ratio,superior ion diffusion,less resistance,and faster electron transport,leading to the substantially improved cycling and rate performance.The MnO2-NRF@CT porous architecture as supercapacitor electrode exhibits outstanding electrochemical performance(961 F g-1 at 1 mA cm-2 in 1 mol/L Na2SO4 electrolyte)and showed good capacitance retention by achieving 92%of its initial capacitance after 5000 cycles.The composite of Cu0.45Mn0.55O2 enhances the specific capacitance up to 983 F g-1 at a current density of 1 mA cm-2 with 90%capacitance retention after 3000 charge-discharge cycles.Square-shaped Mn3O4 nanostructures have been successfully synthesized by hydrothermal method without using any surfactant and achieved 355.5 F g-1 specific capacitance.The specific capacitance was further improved by subjecting reduced graphene(rGO)into Mn3O4 nanostructures.The rGO-Mn3O4 exhibits a high specific capacitance of 457 Fg-1 at 1.0 Ag-1 and good capacitance retention of 91.6%of its initial capacitance after 5000 cycles.