SYNTHESIS AND CHARACTERIZATION OF ZINC OXIDE BASED NANOSTRUCTURES AND COMPOSITES FOR ENERGY RELATED APPLICATIONS

Author

Ahmed Al-Asadi, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2016

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Talapatra, Saikat

Abstract

The main objective of this communication is to report the synthesis and characterization of zinc oxide (ZnO) based nanostructures and composites for energy related applications using a simple and cost-effective chemical bath deposition (CBD) technique. Highly crystalline zinc oxide (ZnO) nanowires (NWs) were synthesized through CBD method using a simple seeding technique. This seeding process includes dispersion of commercially available ZnO nanoparticles through spraying on a desired substrate prior to the CBD growth. A typical growth period of 16 h produced ZnO NW assemblies with an average diameter of ~45 nm and lengths of 1–1.3 µm, with an optical band gap of ~3.61 eV. The NWs growth was successfully achieved on various substrates (e.g silicon dioxide, plastic sheets, copper grid, and carbon nanotube buckypaper). The as-prepared ZnO NWs were found to be photoactive under ultra violet (UV) illumination. UV photosensor devices fabricated using these NW assemblies demonstrated a high photodetection abilities at room temperature under moderate UV illumination power of ~ 250 µW/cm2. These findings indicate the possibility of using ZnO NWs, grown using the same seeding method, for various opto-electronic applications. The same seeding technique was also used to grow ZnO NWs onto aligned multi-wall carbon nanotubes (MWCNTs), which were synthesized by using air assisted chemical vapor deposition (CVD) onto a SiO2/Si substrate. This ZnO NW/MWCNT hybrid structure was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman spectroscopy. The fabricated structure was used as an electrode for supercapacitor (SC) measurements. Good electrochemical performance was accomplished with a specific capacitance of ~192 F/g along with a maximum energy density of ~3.8Wh/kg and a high power density of ~ 28 kW/kg. The fabricated device showed high stability and it retained over 99% of its initial specific capacitance value after 2000 cycles. In addition, we report on the synthesis & electrochemical characterization of two-dimensional Zinc-Aluminum (ZnAl) layered double hydroxides (LDHs) directly grown on Al substrate by using CBD method. After details structural characterization by SEM, Raman spectroscopy, EDS elemental mapping, and X-ray powder diffraction (XRD), the electrochemical performances of an electrode fabricated based on this material were evaluated via cyclic voltammetry and galvanostatic charge-discharge using various electrolytes. The ionic electrolyte device showed a maximum specific capacitance of 120 F/g along with a maximum energy density of 5.17 Wh/Kg and a high power density of 8.4 kW/h. Additionally, we found that a high specific capacitance value of 358 F/g was achieved using an aqueous electrolyte.