Investigation of nanostructured vanadium oxides by wet chemical processing: Structural, morphological, optical, and electrochemical analysis

Material science steers the technological advancements. Even prehistoric ages are called as materials' names. Nano- and thin film materials took place of the normal/bulk materials, nowadays. Thus, in order to product nano-sized/ nano-structured materials and manipulate materials at nano scale, a new discipline is developed, which is called nanotechnology. There are many methods to produce thin films, such as chemical vapor deposition, physical vapor deposition, atomic layer deposition, spray pyrolysis, sol-gel method, etc. Among these methods, sol-gel is one of the most used method because it is economical and easy way. A wet solution, called gel, is obtained with sol-gel method, which is then deposited onto a substrate by some techniques, such as dip-coating, electrodeposition, spin-coating etc. Spin-coating technique is superior among other techniques because it leads to atomic packing in one direction. Nanofibers, which are 1D materials, are one of the most interesting materials among nanostructures due to their versatility, high surface area, high aspect ratio, high porosity, high electrical conductivity in one direction, etc. Electrospinning is most used method to produce nanofibers from lab-scale to industrial scale. However, there are many parameters effecting the characteristics of the obtained fibers in electrospinning technique. Vanadium and its oxide form has been studied for a long time due to their interesting characteristics. The reason of such great interest drawn to vanadium and its oxide forms is based on the varied oxidation states from +2 to +5 which let it form many oxide forms, and also the variability of the oxygen coordination geometries, such as octahedral, square pyramids, tetrahedral etc. These characteristics let vanadium oxides yield an impressive variety of structural and crystallographic arrangements. VO2 exhibits a semiconductor to metal transition near to room temperature, at about 70°C. V2O5 has an orthorhombic crystalline structure with a layered structure, which promises high ratio ion intercalation. Thus, it is very interesting material for electrochemical applications such as li-ion batteries, supercapacitors, sensors, etc. In this study, we prepared eight different vanadium-oxide samples (6 samples in thin-film form, and the other 2 samples in nanofiber form) from three different solutions/gels. We characterized the samples by x-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectrophotometer (UV-Vis), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). Additionally, thermochromic properties of annealed samples were investigated. We also characterized solutions by analyzing their conductivity, surface tension, viscosity and optical properties.