Preparation Of Nano-ATO And Electrically Conductive Composites And Their Electrochemical Properties

Antimony doped tin oxide (ATO) is a light-colored conductive filler with good environmental ability, high temperature stability, chemical erosion resistance, good optical property and mechanical property. The semiconducting material has been used in LCD, solar cell, lithium battery, electromagnetic shielding material and gas sensors. It is still necessary to further investigate the preparation process of nanostructural ATO, such as the effect of Sb doping amount and calcinations temperature on the volume resistivity. It is valuable to conduct the research of the structure, property and conductive mechanism and to understand the relationship between the preparation method and the volume resistivity of the material.At present, gas phase method is usually employed to prepare ATO powder, whereas this method needs expensive raw material and equipments. Co-precipitation method possesses the advantages of simple, cheap and scale-up production. In this thesis, light colored ATO nanoparticles and the ATO nanorods were prepared by co-precipitation method and hydrothermal method, respectively, and the nanostructural ATO exhibits high electrical conductivity. The effect of the synthetic condition on morphology and structure of the nanomaterial was discussed. Based on the powders, polymer composites of ATO/EVA and ATO/polyimide were produced, exhibiting an enhanced conductive property. Composite catalyst Pt-ATO/C was prepared and indicated the good catalytic activity on the anode catalysts for direct methanol fuel cells. The contents are following:1. ATO nanoparticles were prepared by co-precipitation method, the effects of Sb doping amount, calcination temperature and time and pH value on the microstructure and property was discussed. XRD, TG, SEM and TEM were employed to characterize the products. As a result, Sb doping amount and calcination temperature have a significant influence on the microstructure and property. The increase of Sb doping amounts leads to smaller particle size and deeper color, showing the widened peaks in XRD diffraction. Volume resistivity goes down to a minimum value at 5% doping of Sb. High calcination temperature results in a strong XRD diffraction peaks, bigger particle size, deeper powder color and low volume resistivity, and the optimum calcination temperature is 600℃.2. Nanorod clusters of ATO were obtained using hydrothermal method, and the influences of reactant concentration and reaction time on the ratio of length to diameter (L/D) were discussed. Based on the microstructures and morphology measured by means of XRD, SEM and EDS, and formation mechanism of nanorods was proposed. As a result, the concentration of reactants has a slight influence on the L/D; whereas, the increase of the reactants concentration causes the increase of both the diameter and length of ATO nanorod. On the other hand, the reaction time has a slight influence on the diameter of the nanorod, while it obviously affect L/D and the value is up to 10:1 at the reaction time of 20 hr. Volume resistivity of ATO nanorod is about 100Ω·cm, while the value of the material prepared via co-precipitation method is about 2.3Ω·cm.3. ATO/EVA composites were obtained via melting blending and solution mixing blending. Uv-vis spectroscopy and SEM were used to investigate the composites. Compared to melting blending method, ATO prepared by solution mixing method easily distributes in EVA matrix, causing an enhanced mechanical property and conductive property. When ATO loading rises to 15%, volume resistivity reduces to 105Ω·cm.4. Polyimide is one of high performance polymers with high dielectric constant and high temperature resistance. The polymer can be prepared by the synthesis of polyamic acid (PAA) and the following high temperature cyclization. The preparation of ATO needs calcinations at a high temperature, so the nanocomposites can be produced by adding the precursor of ATO into PAA in-situ polymerization method and then the treatment of high temperature. The results show that crystallization of ATO happens during the process of cyclization reaction of the polymer, leading to a reduced agglomeration. Consequently, the nanoparticles are evenly distributed in the matrix, leading to the improvement of the mechanical property.5. Composite catalyst Pt-ATO/C was prepared via co-precipitation method and consecutive polyol process. The Pt-ATO/C electrocatalyst is characterized by XRD, TEM, SEM, EDS and cyclic voltammetry. The composite material shows the excellent catalytic activity and stability in anode catalyst for DMFC. The peak current in forward scan is 8.9 mA·cm-2, which is higher than commercial catalyst. The Pt-ATO/C catalyst exhibits a relatively high activity for the methanol oxidation reaction compared to Pt-SnO2/C or commercial Pt/C catalyst. This activity can be attributed to the high electrical conductivities of the Sb-doped SnO2, which induces the electronic effects with Pt catalysts. Pt-ATO/C is a promising methanol oxidation catalyst with high activity for the reaction in direct methanol fuel cells.