Dr. Viresh Kumar

Thesis Abstract:

Electrochemical energy storage materials and device shave motivated researchers and entrepreneurs due to their high-power capability, longer cycling life, minimum maintenance cost, and rapid charging/ discharging process. However, the low energy density of super capacitors compared to rechargeable batteries limits the application in various sectors. This parameter should be recovered by exploring and modifying electrode materials to encounter the demand. Additionally, exemption of binder facilitated the deposition of active materials on the conducting substrate, and improvement of capacitance has been considered with other crucial performance parameters. Currently, a group of transition metal oxides/hydroxides (TMOs/TM-OH) based supercapacitor electrode materials are investigated as a pseudo capacitive type.

Hence, it comprises the preparation of different metal ferrite MFe2O4(M=Ni,Co&Mn) nanostructure by using chemical route. The structural and morphological properties of metal ferrites were studied. The electrochemical properties were studied and found to be 1380 Fg-1, 972Fg-1 and, 715 Fg-1 for CoFe2O4, NiFe2O4, and MnFe2O4 respectively. Also, an asymmetric device was fabricated and the efficiency was measured using a two-electrode system. In another aspect it deals with the high-performance electrode by preparing bimodal nickel-cobalt-manganese oxide.The nanorod sarray type morphology and crystal structure were studied. The NiCo2O4.MnO2 nanorods delivered remarkable specific capacitance of 2575 Fg-1 (305 mAhg-1) with excellent cyclicretention (92.1%).

The present work also comprises the preparation of Co/Ni hydroxide dots by varying different concentrations of Ni into Co in the ethanol-water medium. By maintaining the concentration of NaOH, and ethanol, which provide their synergetic effect for controlling the exceptional particle growth. The particle size is restricted to around 2.5 nm having a direct band gap of 2.64 eV. The fitting results of X-ray photoelectron spectroscopy suggest the presence of redox couple Co2+,Co3+, Ni2+, and Ni3+ in the hydroxides dots, which facilitates more electroactive sites. The binder-free hydroxide dots showed the maximum specific capacitance around 1926 Fg-1 (221 mAhg-1) ata current density of 1 Ag-1, and exceptional cycling life (~96% up to 20,000). Further, the work also reveals the formation of amorphous metal sulfides with control particle size (~10 nm) by changing the solvent nature (water & ethanol). The effect of sulfide percentage in Co/Ni binary sulfides was studied and tested for electrochemical properties with different molar ratios (0.5M,1M, and 1.5M) of NaOH aqueous electrolyte. Also, the effect of different ions (Na+, K+, Li+) on the electrode properties was carried out.The remarkable specific capacitance was achieved around 2910 Fg-1 at CD of 1 Ag-1 by maintaining outstanding cyclic retention of ~91.5 % even after 10000 cycles.

In addition, the formation of dodecyl sulfate (SDS) functionalized binary Co/Ni (CN) hydroxide was investigated. The developed metal hydroxides possessed a maximum specific capacitance of 2765 Fg-1 at 5 Ag-1 with retained capacity of ~88 % after 5,000 cycles. The efficiency of ASC was evaluated about 283Fg-1by maintaining energy density of 88 Whkg-1.

Keywords:Transition metal hydroxides/ oxides, amorphous, Pseudo capcitance, device fabrication, specific capacitance, specific capacity, cyclic stability