Vanadium oxides based composites for supercapacitor applications

In this thesis, different vanadium-based materials and vanadium/carbon composites were synthesized and explored as active electrode materials for supercapacitor application. The major goal of this study was to incorporate carbon-based materials such as graphene foam and activated expanded graphite into the vanadium-based (oxides and oxynitride) materials to explore their outstanding properties. The as-synthesized vanadium-based materials exhibited high charge storage capacities due to the large stable oxidation states and their layered structures while carbon-based materials presented the much needed specific surface area and good electronic conductivity. The combination of these materials led to the modification of the surface and physical properties of the constituent materials as well as the enhancement of the electrochemical performance for supercapacitor applications. For example, a novel web-like carbon-vanadium oxynitride (C-V2NO) material exhibiting the most unique textural and morphological features generated using the facile synthesis route. The diversity in the structural, morphological, porosity and compositional properties for the vanadium-based materials and vanadium/carbon composites were evaluated by using X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). The electrochemical properties were evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and stability (cycling and floating) tests in both three (3) - and two (2) electrode configurations using an aqueous electrolyte. The composite electrode materials containing carbon incorporated into the pristine vanadium-based material portrayed superior electrochemical properties. Specifically, the asymmetric device of VO2/AEG//C-V2NO where the composite electrode has been adopted as a positive electrode and C-V2NO as a negative electrode, demonstrated a 41.6 Wh kg-1 specific energy and specific power of 904 W kg-1 at a specific current of 1 A g-1. This was the highest device metrics recorded in this study for all vanadium-based devices tested. Thus, the results obtained from this study have clearly established the capability of carefully tuning the synthesis conditions for obtaining electrochemically active nanostructured electrode materials such as web-like carbon-vanadium oxynitride (C-V2NO) materials as promising candidates for supercapacitor applications. In this thesis, different vanadium-based materials and vanadium/carbon composites were synthesized and explored as active electrode materials for supercapacitor application. The major goal of this study was to incorporate carbon-based materials such as graphene foam and activated expanded graphite into the vanadium-based (oxides and oxynitride) materials to explore their outstanding properties. The as-synthesized vanadium-based materials exhibited high charge storage capacities due to the large stable oxidation states and their layered structures while carbon-based materials presented the much needed specific surface area and good electronic conductivity. The combination of these materials led to the modification of the surface and physical properties of the constituent materials as well as the enhancement of the electrochemical performance for supercapacitor applications. For example, a novel web-like carbon-vanadium oxynitride (C-V2NO) material exhibiting the most unique textural and morphological features generated using the facile synthesis route. The diversity in the structural, morphological, porosity and compositional properties for the vanadium-based materials and vanadium/carbon composites were evaluated by using X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). The electrochemical properties were evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and stability (cycling and floating) tests in both three (3) - and two (2) electrode configurations using an aqueous electrolyte. The composite electrode materials containing carbon incorporated into the pristine vanadium-based material portrayed superior electrochemical properties. Specifically, the asymmetric device of VO2/AEG//C-V2NO where the composite electrode has been adopted as a positive electrode and C-V2NO as a negative electrode, demonstrated a 41.6 Wh kg-1 specific energy and specific power of 904 W kg-1 at a specific current of 1 A g-1. This was the highest device metrics recorded in this study for all vanadium-based devices tested. Thus, the results obtained from this study have clearly established the capability of carefully tuning the synthesis conditions for obtaining electrochemically active nanostructured electrode materials such as web-like carbon-vanadium oxynitride (C-V2NO) materials as promising candidates for supercapacitor applications. In this thesis, different vanadium-based materials and vanadium/carbon composites were synthesized and explored as active electrode materials for supercapacitor application. The major goal of this study was to incorporate carbon-based materials such as graphene foam and activated expanded graphite into the vanadium-based (oxides and oxynitride) materials to explore their outstanding properties. The as-synthesized vanadium-based materials exhibited high charge storage capacities due to the large stable oxidation states and their layered structures while carbon-based materials presented the much needed specific surface area and good electronic conductivity. The combination of these materials led to the modification of the surface and physical properties of the constituent materials as well as the enhancement of the electrochemical performance for supercapacitor applications. For example, a novel web-like carbon-vanadium oxynitride (C-V2NO) material exhibiting the most unique textural and morphological features generated using the facile synthesis route. The diversity in the structural, morphological, porosity and compositional properties for the vanadium-based materials and vanadium/carbon composites were evaluated by using X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS). The electrochemical properties were evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and stability (cycling and floating) tests in both three (3) - and two (2) electrode configurations using an aqueous electrolyte. The composite electrode materials containing carbon incorporated into the pristine vanadium-based material portrayed superior electrochemical properties. Specifically, the asymmetric device of VO2/AEG//C-V2NO where the composite electrode has been adopted as a positive electrode and C-V2NO as a negative electrode, demonstrated a 41.6 Wh kg-1 specific energy and specific power of 904 W kg-1 at a specific current of 1 A g-1. This was the highest device metrics recorded in this study for all vanadium-based devices tested. Thus, the results obtained from this study have clearly established the capability of carefully tuning the synthesis conditions for obtaining electrochemically active nanostructured electrode materials such as web-like carbon-vanadium oxynitride (C-V2NO) materials as promising candidates for supercapacitor applications.Thesis (PhD)--University of Pretoria, 2019.PhysicsPhDUnrestricte