Conducting Polymer Nanocomposites for Supercapacitors

Abstract

Supercapacitors have attracted more interest of researchers due to its high power density, fast charging-discharging rate and excellent long cycle life. Recently, conducting polymers (CPs) have been explored for elech'ochemical applications and supercapacitor is one of them. The advantage of using CPs is that they are environmentally friendly and exhibit high specific capacities while being able to deliver energy at a relatively rapid rate as short path lengths for ionic transport allow faster ionic diffusion within the CP network. However, the major disadvantage ofthe CPs when used as supercapacitor electrode is poor cycle life which limit its application as individual electrode material. This is unavoidable, because CPs swell and contract substantially on charge and discharge, respectively as anions or cations are doped or un-doped into the CP. In order to alleviate the limitation, among other strategies reinforcing the CPs with other materials such as carbon based materials (e.g., graphene, carbon nanotubes), inorganic oxides (e.g., Mn02, Sn02, Ti02), sulfides and hydroxides and other metal compounds have been proved to be attractive to enhance cyclic stability and capacitance value of CPs. Hence it is desirable to explore suitable CPs composite materials for supercapacitor applications. This thesis is mainly focused on the use of composites of CPs as electrode materials of supercapacitors. In this regard mesoporous silicon (mSi) obtained by the magnesiothermic reduction of mesoporous silica was used to deposit Polyaniline (PANI) in its pores, the composite was tested for its charge storage application as high performance supercapacitor electrodes. Structural and morphological properties of synthesized nanostructures were explored by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis and Fourier transmission IR spectroscopy (FT-IR). BET surface area of synthesized mesoporous silicon is among the highest for porous silicon prepared/ reduced from silica. FUliher the electro!)hemical charge storage perfonnance of mesoporous silicon/ polyaniline composite, mesoporous silica! polyaniline composites, mesoporous silicon, mesoporous silica and polyaniline were evaluated and compared with each other by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCCD). Enhanced electrochemical performance of iii mesoporous silicon! polyaniline composite is attributed to the high surface mesoporous morphology of mesoporous silicon with a network structure containing abundant mesopores enwrapped inside electrochemically permeable polyaniline matrix. Fmiher mesoporous polyaniline was successfully synthesized by facile and cost effective method using surfactant during in-situ polymerization reaction. Then mesoporous silicon! mesoporous polyaniline composite was synthesized to compare its charge storage performance for supercapacitor electrode with mesoporous polyaniline. The structural and morphological properties of prepared nanostructures were explored by X-ray diffi-action (XRD) , scanning electron microscopy (SEM), and Fourier transmission IR spectroscopy (FT -IR). Further the electrochemical charge storage perfonnance of mesoporous silicon/ mesoporous polyaniline composite, mesoporous silica! mesoporous polyaniline composites and mesoporous polyaniline were evaluated and compared with each other and with their counterpart composites with simple polyaniline by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCCD). Conducting mesoporous network of polyaniline in the form of mesoporous silicon/ mesoporous polyaniline composite enhances the electrochemical storage performance as compared to mesoporous silicon/ polyaniline composite electrode. Fmiher molybdenum disulfide (MOS2) and molybdenum oxide (M003) synthesized by thermal decomposition of molybdenum dithiocarbamate were utilized along with graphene nanoplatelets (GNPs; of grades M5) to synthesized polymer nanocomposites using polyaniline (PANI) and polypYlTole (PPy). Fonnation of molybdenum dithiocarbamate complex was confi1111ed by elemental analysis and Fourier transmission Infra-red spectroscopy (FT -IR). Thermogravimetric analysis (TGA) of molybdenum dithiocarbamate complex was done to confirm the temperature to decompose it into desirable MOS2 and Mo03. Structural and morphological properties of prepared MOS2 and M003 series of nanocomposites along with respective MoS2 and Mo03 constituent were explored by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Fmiher the electrochemical charge storage performance of composites and used constituents were evaluated and compared with each other by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge