Electrochemical Synthesis And Properties Of Tungsten Oxide/Polyaniline Composites

Conducting polymer based organic-inorganic composite materials have attracted considerable attentions in recent years. They can not only combine the advantages of the two components and exhibit their synergistic effect, but also can improve the stability of inorganic moieties through organic-inorganic interactions. Tungsten oxide (WO3) is an attractive inorganic material which can be used in eletrochromic devices, gas sensors and photoelectrochemical systems. However, the poor stability of WO3film due to its solubility in aqueous electrolyte restricts its commercial application. Polyaniline (PANI) is a promising candidate for immobilization of inorganic particles owing to its inherent reversible redox property, ease of fabrication and good chemical stability. The stability of WO3can be improved through distribution of the oxide particles in the matrix of the PANI. The electrochemical activities can be enhanced through organic-inorganic interactions as well. Thus composite materials of PANI and WO3deserve investigation in both theoretic and application research.In this thesis, composite films of PANI and WO3were fabricated by electrochemical codeposition on carbon cloth. Electrochemical sensoring of WO3/PANI composite modified electrode for several inorganic molecules including iodate, bromate, chlorate, nitrite and organic molecule of4-nitrophenol were studied. Pseudocapacitive performance of WO3/PANI film was also studied in detail. In addition, surfactant directed and pseudocapacitive properties of nanostructured WO3/PANI composite films were investigated. This dissertation is focused on the following points:1. WO3/PANI composite modified carbon cloth was fabricated by cyclic voltammetry (CV) from a solution of aniline and tungstic acid. The WO3/PANI composite were charactrerized by scanning electron microscopy (SEM), energy dispersive X-ray diffraction (EDX), FT-IR and CV. The obtained WO3/PANI film displayed a significant enhancement of electrocatalytic activity for iodate reduction and a better stability than that of individual WO3and PANI films due to the contribution of two components and the uniform distribution of WO3in PANI. Result of amperometric experiment revealed a good linear relationship between response current of the modified electrode and concentration of IO3from20μM to500μM, with a high sensitivity of0.54μA/μM and a detection limit of2.7μM for the determination of iodate. This composite film was successfully applied in determination of iodate in commercial table salt. The results exhibit a good agreement with the results of the conventional iodometic method with the relative error of less than3.6%.2. Cyclic voltammetry, chronoamperometry and square wave voltammetry were used to investigate electrocatalytic reductions of BrO3-, ClO3-, NO2and4-nitrophenol on carbon cloth modified by WO3/PANI composite film. Results of amperometric experiments on WO3/PANI modified electrode reveal good linear relationship between response currents of the electrode and concentration of BrO3-, ClO3, NO2-and4-nitrophenol in the range of40μM～1.2mM,0.12mM～20mM,40μM～2.50mM and50μM～400μM, respectively. The sensitivity and the detection limit (S/N=3) for these species are0.202μA/μM,3.5μM (BrO3-);0.035μA/μM,23μM (C1O3-);0.120μA/μM,5.9μM (NO2-) and0.443μA/μM,8.8μM (4-nitrophenol). The WO3/PANI composite film exhibits the higher catalytic activities toward electrochemical reduction of BrO3-and NO2due to their synergistic catalytic effect of WO3and PANI.3. A carbon cloth electrode modified with CU/WO3/PANI composite was prepared by electrochemical deposition of Cu particles on WO3/PANI composite film. The morphology and electrochemical properties of the composite were evaluated by SEM, CV and linear scan voltammetry (LSV). The results demonstrate that the porous CU/WO3/PANI exhibit higher electrocatalytic activity for nitrate reduction than that of dense film of Cu particles modified on carbon cloth. The nitrate reduction current on CU/WO3/PANI is linearly related to nitrate concentration over the range40-280uM with a sensitivity of4.5μA/μM and the detection limit (S/N=3) of1.2μM. The composite film is tried to be used for detection of nitrate in water sample with R.S.D of3.8%evaluated by three repetitive measurements.4. Composite films of WO3/PANI were fabricated by cyclic voltammetry from a mixed solution of aniline, tungstic acid and H2O2. Surface morphology and chemical composition of WO3/PANI composites were characterized by SEM and X-ray photoelectron spectroscopy (XPS). CV, chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) results show that WO3/PANI composite film exhibit good pseudocapacitive performance over the potential range of-0.5to0.7V vs. SCE with the specific capacitance of168F/g at current density of1.28mA/cm2and energy density of33.6Wh/kg, which is91%higher than that of similarly prepared PANI (17.6Wh/kg). An asymmetric model capacitor using WO3/PANI as negative and PANI as positive electrodes over voltage range of1.2V displays a specific capacitance of48.6F/g and energy density of9.72Wh/kg at the power density of53W/kg, which is two times higher than that of a symmetric capacitor modeled by using two PANI films as both positive and negative electrodes.5. Nanostructured WO3/PANI composites were synthesized by cyclic voltammetry using sodium dodecylbenzenesulfonate (SDBS) surfactant as a template. Surface morphologies and chemical composition of WO3/PANI composites were characterized by SEM and FT-IR. The pseudocapacitive behaviors of composite films were investigated by CV and CP. The nanostructured WO3/PANI composite exhibits good pseudocapacitive performance over a wide potential range of-0.5to0.65V vs. SCE with energy density of41Wh/kg at power density of650W/kg and energy density of30and25.6Wh/kg at power density of5kW/kg and10kW/kg, respectively. In comparison, the composite film prepared without using SDBS surfactant template has an energy density of26Wh/kg at power density of650W/kg and17.8Wh/kg at5kW/kg.