Elecrochemical Preparation, Characterization Of Fluorinated TiO₂ And WO₃ Thin Film And Their Photoelectrochemical Performance

The rapid development of photochemical systems has attracted many researchers to investigate a new way for securing the future supply of clean and sustainable energy.One of the most promising semiconductors for photoelectrochemical applications is TiO₂.However,TiO₂ can be excited only under illumination with UV light at wavelengths of less than 388nm because of the wide band gap(3.2 eV) of the anatase structure.Only 3-5%of the solar radiation that reaches the earth's surface exists in the UV region;indeed,the quantum yield of the TiO₂-based reaction achieved so far is still very low(typically less than 0.1).Therefore,further improvement of TiO₂ photoactivity is undoubtedly needed.This thesis includes two parts.In part one,TiO₂ thin film electrodes with photoelectrochemical(PEC) and photocataltie(PC) properties were prepared by anodic potential oxidation or sol-gel method.A new and simple method for surface fluorination of TiO₂ films is presented by anodization in HF aqueous solution.The prepared samples have been characterized for morphology by scanning electron microscopy(SEM).X-ray diffraction(XRD).UV-vis diffuse reflectance spectroscopy(DRS),X-ray photoelectron spectroscopy(XPS),photoluminescenee(PL) respectively.The PEC property of the TiO₂ thin film sample was investigated by using stand-state photocurrent method and photocurrent action spectrum experiments.Mott-Schottky plots were also used to analyze the possible.PC properties were investigated by degradation of X3B as target pollution.As a result,all the prepared samples with different methods have a improvement on photocurrent,although with various degree; the incident photon to current efficiency(IPCE) of the fluorinated TiO₂ thin films was also improved;The band energy narrowed from 3.22 to 3.10e V.The PEC performance and PC activities for the degradation of X3B were highly enhanced.The possible masons for such an improvement were studied in detail.It is mainly attributed to the negative shifted energy band edges.In part two,a new and simple method of electrochemical etching in acidic aqueous solutions that contain fluorine for the electrodeposited WO₃ thin films is presented.The samples were characterized by photoelectrochemistry,scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),UV-Vis diffuse reflectance spectroscopy and photoluminescence (PL),respectively.Results showed that the etching increased the specific surface area with a concomitant reduction in the catalyst mass and also a change in the surface status of the electrodes.This modification of the surface status improved the photoelectrochemical performance of the electrodes under visible and UV-Vis light illumination with the same mass and specific surface area.This enhancement can be ascribed to the surface fluorination of the electrodes that result in a decrease in the surface recombination centers and a negative shift in the flatband potential.The light absorption and crystalline were found to be unchanged by etching.The etched WO₃ film electrode shows excellent photoelectrochemical stability in acid solutions.This provides a novel method for increasing the photon electric conversion efficiency of WO₃ thin filmelectrodes.