The Super Capacitor Electrode Materials Based On Duplex Stainless Steel Mno < Sub > 2 < / Sub > Preparation And Its Performance Study

Supercapacitors, with a combination of high power density and high energy density, have been extensively studied in the past decades. Although the specific capacitance (SC) of RuO2based supercapacitor is relatively higher, the high cost and toxic nature inhibit its commercial use. The natural abundance of MnO2and its environmental compatibility make it a promising material for use in supercapacitor. Results from literatures showed that the properties of MnO2were associated with the preparation methods, morphologies as well as the testing conditions. Generally, MnO2works in aqueous system composed of alkaline salt. The corrosion of current collector was an important issue. Most studies were focused on graphite and nickel, little attention was paid on the stainless steel which has a best combination of good corrosion resistance and high mechanical strengh.In this thesis, the properties of MnO2based on stainless steel were investigated. The deposition mechanism of MnO2was studied by linear sweep voltammetry combined with X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The electrochemical characteristics of MnO2were investigated by cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectrum (EIS). Results showed that:The deposition process of MnO2was controlled by the diffusion of Mn2+. The current peak followed an Arrhenius relationship with the temperature, while the onset potential of MnO2deposition had a linear relationship with the temperature. XRD demonstrated the as prepared MnO2was amorphous in nature. XPS and EDX revealed that the MnO2was hydrated. The surface of MnO2was nano-sized structure, controlled by the substrates and deposition potential. With the increase of deposition potential, the3D network structure was evolved to nano-rod structure, and the length was decreased as well.The SC of MnO2based on2304duplex stainless steel was higher than that of based on2507duplex stainless steel. The capacitance was increased with the increase of load mass, while the SC was decreased. The minimal SC was obtained when the deposition potential was0.8V. The SC was aroused with the increase of concentration of Na2SO4, and saturated at0.5M. The surface morphologies were changed during the whole charge-discharge cycling. The surface morphology of MnO2based on2304 duplex stainless steel was evolved from nano-rod into nano-pedal. The SC was improved due to the morphological evolution, and was stable after3000charge-discharge cycling.The operating temperature had a significant impact on the SC of MnO2. The SC was increased with the elevation of temperature. The EIS results showed that the increase of operating temperature improved the conductivity of electrolyte and decreased the charge-transfer resistance (Rct). There is an Arrhenius relationship between the Rct and T. Under high operating temperature, the dissolution and re-deposition of MnO2was accelerated, and the morphology was evolved from nano-rob into nano-sheet. The highest SC of950F/g was obtained after260charge-discharge cycling. Although the SC was improved, the stability was worsened. According to the results, MnO2should not work at high temperature.