Sharif Digital Repository

ZnO is a wide and direct band gap (3.37 eV) semiconducting material with a large exciton binding energy (60 meV). It has been extensively studied in the last few years owing to its potential applications in various fields such as surface acoustic wave devices (SAW), transparent electrode, solar cell windows, photovoltaic devices, gas sensors and photoelectrochemical cells. Recently, much attention has been paid to rare-earth (RE) doped ZnO for possible applications in visible emitting phosphors in displays, high power lasers, and other optoelectronic devices. In this thesis, initially ZnO thin films were deposited on glass and ITO substrates using sol-gel dip-coating method. Optical and... 

According to the growth in the world population and the decrease in fossil fuels resources and also according to the pollution caused by these unrenewable resources, using hydrogen as an alternative energy resource seems to be unavoidable. In the past decades, semi-conductor metal oxides were being used widely in the energy domain of study, due to their appropriate band gap in the ultra-violet and visible spectra. Among these metal oxides, ZnO has been under special attention because of its electron mobility and its reasonable production cost and also its friendliness to environment. But the high band gap of ZnO (3.2 eV) has impeded its use in visible light spectrum. In this project,... 

In this project, the photoelectrochemical properties of ZnO nanostructures modified by CdS and Graphene was studied. Firs, titanium foil was cut into rectangular shape with 1cm width and 3 cm length, cleaned by rinsing in acetone and ethanol and annealed at 4000C for an hour. As a result, a thin layer of titanium oxide was formed on Ti sheet. Then a layer of grapheme oxide was deposited on substrate using Electrophoretic deposition (EPD). After that, ZnO nanostructure was deposited on the TiO2 substrate using Electropulsation (EP) with 20 consecutive pulse followed by 3 minutes Electrodeposition (ED). Using SEM analysis, the morphology of ZnO was determined to be nanopetals in which the... 

WO3 have good electrochromic, gas sensor, photocatalyst, phoelectrochemical (PEC) properties. due its properties, tungsten oxide have many application in technology and industry. In this thesis, pure WO3 thin film and MWCNT-WO3 nanocomposite thin films with different weight percent of MWCNT/WO3 utilize for energy domain, particular hydrogen production with phoelectrochemical reactions spiliting water. For this purpose, initially WO3 thin films were deposited on glass and ITO substrates using sol-gel dip-coating method. Optical and surface properties of the films dried at 100ºC and annealed at 400 ºC had been investigated. UV-Visible spectrophotometer, atomic force microscopy (AFM), X-ray... 

The 21st century is facing two major obstacles on the way of accessing clean and renewable energies: first, the rapidly increasing need to the energy resources; and second, the limitations - as well as side-effects - of the conventional fossil fuels. Meanwhile, the production of the solar hydrogen, through water splitting, has been proposed as a promising solution to find a clean and effective source of energy. This process occurs in photo-electro-chemical systems with the activation energy that lies within the range of visible light. One approach that herewith comes to mind, is to start the process by utilizing semiconductors to absorb the sunlight. In order to overcome the overpotential... 

Growing demand on energy and limitation and consequence of fossil fuels have caused to utilize the clean and renewable energy sources. Hydrogen is a clean energy carrier which produced just water vapor during combustion. Today, methods which are usually used to produce this fuel are based on using fossil fuel compounds. Therefore, utilizing new production methods is unavoidable. One of these methods is using semiconductors such as TiO2 to spilt water and produce H2 by solar irradiation. Reducing the energy gap of these semiconductors to match the solar spectrum, specially in its visible range, modification of their structures, surfaces and stability are the main challenges in hydrogen... 

Currently, fossil fuels are the primary source of energy in the world. The increasing human need for energy and the limited resources of fossil fuels and their environmental side effects necessitate the search for other sources of energy. Considering its abundance and eco-compatibility, using solar energy is one of the best candidates for future. One of the methods to use solar energy is to convert and store it as hydrogen fuel by photoelectrochemical cells. In recent years, the main challenge with the production of hydrogen fuel in photoelectrochemical is optimizing them to increase efficiency. For this purpose, various approaches have been proposed such as the fabrication and use of... 

World population growth, depletion of fossil fuels resources depletion and increased air pollution resulting from their consumption, human society has had to replace fossil fuels with renewable sources. In this context, the production of hydrogen using solar energy is feasible candidate to replace fossil fuels, which can be produced by water splitting in a photoelectrochemical (PEC) cell using an appropriate photocatalyst. This clean production method has been attended by many researchers in recent years. The most common photocatalyst for the conversion of sunlight to hydrogen by splitting water is Titanium dioxide (TiO2). But high energy gap and fast electron-hole recombination rate in TiO2... 

Free-standing TiO2 nanotube array (TNA) films were fabricated via two-step anodization of titanium sheet. The electrolyte consisted of DI water and ethylene glycol (99.9%, Merck) solution with volume ratio of 10:90, containing 0.5 M NH4F. Then, a few drops of 1M H3PO4 aquaes solution have been added to adjust pH at 5.7. The anodization process was performed at optimized applied voltage of 60 V for 200 min. Indeed it does in two-step for 50 and 150 min, and samples were sonicated of 40s between two steps. Then, to crystallize the grown structures, they were annealed in air at 500˚C for 80 minutes. Surface of TNA was modified by sequential-chemical bath deposition (S-CBD) method to fabricate... 

In this research, initially, thin film of TiO2 nanotube arrays (TNA) was deposited on Titanium foil (Ti), using anodization technique under an optimized applied voltage of 60 V, for 200 minutes. Highly smooth and ordered TNA formed by effective two-step anodization method. The TNA synthesized by this procedure, showed a better surface smoothness and tube order as compared with the TNA prepared in one-step anodization process. The electrolyte which was utilized for the anodization process, contained 90% of Ethylene Glycol (EG) in volume, 10% de-ionized water (DI) in volume, 0.1M Ammonium Fluoride (NH4F), and 0.5 ml Phosphoric Acid (H3PO4) 1M in order to adjust the pH about 5.6. Moreover, the... 

Dye sensitized solar cells (DSCs) are among the 3rd generation solar cells which their mechanism of light absorption is similar to chlorophyll in green leafs and is based on photo-excitation of dyes. The electron-hole pairs of photo-excited dye separate at the interface of mesoporous semiconductor-dye-electrolyte. One of the approaches to increase the light path length and therefore the light harvesting efficiency in DSC is the addition of light scatterers inside the mesoporous semiconductor (photoanode).In this research, nanoparticulated hollow TiO2 fibers are introduced as novel light scatterers in DSCs with simultaneous light scattering, light trapping and high surface area. Light... 

The optimized geometry and structure of iron oxide(Fe2O3) nanorod arrays as the photoanodes of photoelectrochemical cells have been calculated. Using finite element method, different structures have been studied in order to maximize the photocurrent density generated by the photoanodes. Two main characteristics of nanorod arrays namely the aspect ratio of nanorod and the density of nanorods in array have been selected as the variables. The absorbance of the photoanode has been calculated using Electromagnetic Waves Physics in COMSOL Multiphysics software. In this study, nanorods with aspect ratio of 3.6 to 40 have been varied and compared. The results reveal that the current density has a...