Development of Nickel-Based Hybrid Metal Oxide Nanocomposite Electrodes for Advanced Electrochemical Supercapacitor and Electric Field Emission Application

Abstract

This thesis work preferentially motivates us to investigate intriguing electrochemical energy storage performance of some innovative nickel based hybrid metal oxides nanocomposite which have been rarely studied so far. Besides, some other nickel based transition metal oxide compounds have been publicized first time their potential field emission response for future application. Various dynamic synthesis protocols i.e. co-precipitation, sol-gel, and ultra-sonication have been adopted to prepare hierarchical surface morphology which can boost up electrochemical and FE performances. The enhanced properties of the assynthesized nanoparticles and their composites have been explained in terms of synthesis techniques, surface morphology, electrode and electrolytic properties, and process control. The aforementioned work has been described systematically in six different chapters as follows: Chapter I accentuates a brief introduction to electrochemical supercapacitors and their classification, components and materials, performance & testing, theoretical model of field emission and FE parameters, and their applications etc. Additionally, the theory of DFT and important parameters (i.e. work function, quantum capacitance) related to our experiment has been discussed briefly. The motivation, literature survey, and objective of our nanomaterials used for performance testing have been disclosed. Chapter II provides a detailed description of the synthesis protocols used to synthesize our chosen compounds and their carbon-based composites have been illustrated schematically. The basic theory of experimental techniques used for the structural, morphological, electrochemical, and FE characterization of as-prepared samples was also demonstrated with a diagram. Chapter III deals with the primary characterization results (i.e. XRD, Raman, FTIR, FESEM, TEM, EDS, BET etc.) with electrochemical response of two compounds core@shell NiCo2O4@MnO2 and NiMnO3/NiMn2O4 nano-cotton and their performences further upgraded with inclusion of MWCNT. The electrochemical response (CV, GCD) was observed at different scan rates and current densities using glassy carbon as the working electrode and 3 M KOH as an electrolytic solution. High specific capacitance 824 Fg-1 and 869 Fg-1 was observed for core@shell and nano-cotton and its value further upgraded 1048 Fg-1 and 1037 Fg-1 due to incorporation of MWCNT respectively. Good cyclic stability between ~82.6%-93% was examined over 5000 cycles for all compounds and EIS spectrum before and after testing was inspected. Chapter IV represents the primary experimental results of three nickel based transition metal oxide (NiMn2O4, NiCr2O4, and NiO [CdO]2) with unique nano morphology, high phase purity, balanced stoichiometry, and exclusive surface morphology for FE characterization. The field emission features including current density (J) electric field (E), FN plots, long stability were studied over long period and field enhancement factor (β) 3381, 2074, and 1854 were determined. The DFT calculation was also performed to calculate work function (Ф) using the supercell approach for the calculation of field enhancement factor (β). Chapter V covers the structural, electrochemical, field emission, and in-depth DFT study of two other productive compounds La2NiO4 and NiGa2O4 and further compared with La2NiO4/CNT and NiGa2O4/r-GO respectively. Preceding primary characterization was carried out to confirm their crystal symmetry, elemental indication, and hierarchical porous morphology. The electrochemical and field emission response was examined and compared. Good specific capacitance 426 Fg 1 and 643 Fg-1 was discovered for La2NiO4/CNT and NiGa2O4/r GO in 1M KOH electrolytic solution and Ni foam as a working electrode with capacitance retention 93% and 99.1% over 5000 cycles. Besides, improved field enhancement factor 4144 and 4429 was estimated for their CNT and r-GO based composite FE electrodes. The DFT study reveals exciting features related to charge transfer due to orbital interaction, enhanced electronic states near Fermi level for their carbonous composites leading to enhanced conductivity, increased mobility of electrolytic ions in the open space of CNT or r GO. The lower work function and higher quantum capacitance support the improved charge storage performance and field emission response. Chapter VI concludes the work carried out in the thesis with their future scope. The electrochemical performance and field emission characteristics of all compounds have been compared and discussed best outputs from our research with merits and demerits.