Sharif Digital Repository

In the present work, edge-functionalaized graphene was used as electrode material and its electrochemical properties were systematically characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Two methods were applied to modify the gold electrode surface. First method was the self assembling process of graphene nanosheets on gold electrode surface. Second method was simply casting specific amounts of graphene suspension on the gold electrode surface. Nyquist plots show decrease of the charge transfer resistance on the electrode surface at both cases. In cyclic voltammetry studies, first electrode shows no significant changes while the second electrode exhibits... 

Supercapacitors represent a new class of energy storage devices that have been attracted many researchers in last few years. Graphene with unique properties such as superior electrical conductivity and large specific surface area is one of the most suitable materials in supercapacitor applications. Besides, metal oxides are being used as active compounds in supercapacitors due to their role in redox reactions. In this research, synthesis and characterization of supercapacitor electrodes based on graphene and MnO2 nanostructured materials was studied under different conditions. For this purpose, Graphene oxide (GO) was synthesized by Hummers’ method and then, it was deposited on a nickel foam... 

During the past two decades, much attention has been paid to rechargeable lithium batteries, because they have high energy density. Glass-ceramics is a category of this material, which may be of great potential as solid electrolytes.. The object of this thesis is preparation of Li2O-TiO2-P2O5 glass, glass-ceramic and investigation their electrical behavior. Prepared Samples were investigated by Differential thermal analysis (DTA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-Visible spectroscopy and Electrochemical impedance spectroscopy (EIS). In this study LiTi2(PO4)3 crystals were crystallized in a glass with the composition 45Li2O-25TiO2-30P2O5 (molar ratio). According... 

Impedance measurement is one of the most efficient electrochemical methods to investigate the mechanism and kinetics of electrode reactions. This method can detect the steps of successive or parallel electron and mass transfer chemical reactions based on measuring the response time constant. The method of showing results, commonly known as Nyquist diagram,which is based on drawing real and imaginary components of the impedance, with respect to each other in different measurement frequencies, is very useful for determining the mechanism of electrode reactions and the kinetic measurements. The main objective of this thesis is totheoretically determine the impedance response of six... 

Plasma Electrolytic Oxidation is a new and promising method for synthesis of oxide layers and coatings on light metals such as titanium and aluminum. This method is a fast, easy and economicalway to produce TiO2 layers on Ti substrate. Photocatalytic properties of TiO2 can be improved with doping of other elements such as metals and non-metals by expanding its band gap which is in UV area of light spectrum in to visible area.Photocatalytic properties of TiO2 is also dependent on surface area and grain size, oxide layers which has been produced with PEO process has a high surface area due to its porosity. Voltage, electrolyte and additives concentration are among parameters which can affect... 

In the first part, metallic nanoparticles were synthesized on the different carbon nanostructers platform such as nanodiamond and graphene sheet using electrochemical and chemical methods. The prepared composite film were characterized by electron microscopy, spectroscopy and electrochemical techniques. The synthesized nanocomposite were applied as a modifier in order to prepare electrochemical sensors for determination trace amount of important pharmaceutical and biological compounds.In the first work, Nanodiamond-graphite (NDG) decorated with Ag nanoparticles (AgNPs-NDG) was synthesized with chemical method. The surface morphology and the nature of the composite were investigated. The... 

In recent years lithium-air batteries captured worldwide attention because of their high energy density. Solid state electrolytes is one of the main components of lithium-air batteries. Lithium almunium titanium phosphate(LATP) is a nasicon type ion conduction which may be of great potential as solid electrolyte. The object of this thesis was the preparation of LATP solid electrolyte which can be used in a lithium-air battery. To reach this goal LATP powder was synthesized using a solution-based method and an appropriate crystallization temperature was selected based on obtained results of X-ray diffraction analysis. In the next step solid electrolytes was prepared under different pressing... 

As one of the main features of Li-Ion batteries, internal resistance severely affects performance and characteristics of these batteries e.g. output power and working voltage. In this study, we tried to understand role of internal resistance on microstructure development and provide a correlative relation between microstructural features and performance of lithium-ion batteries. To catch this target, four types of Li-Ion battery chose, varying cathode type. These batteries were exposed to both normal and severe cycling conditions. Regarding to the key role of current rate on the performance of Li-ion batteries, an extensive research on different types of batteries at various current rates... 

In this thesis, pure –known as T- and chromium doped titanium dioxide nanoparticles –known as -CTx- with different dopant atomic ratio (0.1 to 5 %at.) were synthesized using a facile, fast and efficient method. FESEM and XRD studies showed no morphologic and structural change via Cr doping of nanoparticles (size in the range of 20-30 nm). However, according to DRS analysis, Cr intrusion in TiO2 crystal structure, drastically reduced band gap energy of pure TiO2 from 3.14 eV to 1.81 eV for CT3 powder and improved absorption range of UV-Vis spectrum. Mott-Schottky plots indicated that, Cr doping, caused reduction in donor density of TiO2 and an upward shift in the conduction band edge....