Nanocomposite Materials for High-Performance Electrochemical Supercapacitors

Abstract

Electrochemical supercapacitors (ESs) are one of the most modern energy storage systems that offer a balance between power and energy densities in which the energy storage mechanisms could be an electrostatic double layer (EDLCs) and pseudocapacitive. In this thesis, hybrid asymmetric supercapacitors have been developed to optimize the advantages for different types of (ESs) such as high conductivity, stability, fast charge-discharge, and relatively high performance. These developments include high active mass loading electrodes based on multiwall carbon nanotubes (MWCNTs) and transition metal oxides with incubation of low binder percentage and a high mass loading of 40 mg cm-2 that guarantees high electrochemical performance at a wide potential range for different electrodes, especially the cathodic one. Novel synthesis techniques and different multi-dispersants have been demonstrated; a conception colloidal fabrication method has been developed to improve the morphology/dispersion for composites of Fe3O4/MWCNTs (M-CNTs) and NiFe2O4/MWCNTs. Firstly, an advanced synthesis method called particle extraction through a liquid-liquid interface (PELLI) has been developed to enhance the dispersion of the nanoparticles M-CNTs. Furthermore, palmitic acid (PA) has been used as a surfactant in the bottom-up (PELLI) to reduce the agglomeration of M-CNTs with high Gamma (𝛾𝛾) ratio (nanoparticles/MWCNTs). Moreover, different synthesis methods have been developed in the presence of celestine blue dye (CB) as a co-dispersant with advanced electrostatic interaction and coagulation mechanism that ensured well- dispersed of (Fe3O4, NiFe2O4) coated (MWCNTs) at high mass loading. Subsequently, more optimizations have been done to analyze the effect of different adsorption mechanisms by using other co-dispersant agents such as pyrocatechol violet (PV), azure A chloride (AA), and m-cresol purple (CP). Finally, cyclic voltammetry, galvanic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic stability have been done for the fabricated electrodes and devices in neutral aqueous electrolytes that showed a relevant electrochemical performance in a large potential range.