PSS, PEG Modified PEDOT/Inorganic Composite Materials And Their Thermoelectric Properties

As the world’s demand for energy is causing a dramatic rise in social and the serious environmental problems caused by the combustion of fossil fuel, sustainable energy conservation technologies are attracting significant attention. Thermoelectric (TE) material is a kind of "green" and functional material employed in power generation and refrigeration, can directly achieve the conversion of electrical energy and thermal energy taking advantage of industrial waste heat and renewable energy, have good energy saving and environmental benefits. To date, most studies on high-efficiency TE materials have mainly focused on the field of inorganic semiconductors. However, the high cost of raw materials and production facilities as well as heavy-metal pollution considerations and the poor processability of inorganic semiconductors are limiting their wide application to TE systems. Conducting polymers have been paid much attention because of their low density, low cost, relatively simple synthesis, and easy processing into versatile forms.Poly(3,4-ethylenedioxythiophene)(PEDOT) and its derivates will be a promising candidate for organic TE materials because of their high electrical conductivity, low thermal conductivity, good environmental stability, and unique "metallic and non-metallic" performance. Currently, an increasing number of studies have reported on the TE performance of PEDOT:PSS/inorganic composite materials, including PEDOT:Tos, PEDOT/PbTe, PEDOT:PSS/SWCNTs, PEDOT:PSS/Graphene, PEDOT:PSS/Ca3Co4O9et al. The value of ZT can be as high as0.42, which is comparable to that of Bi2Te3. These reports have proved that conducting polymer/inorganic micro-or nano-TE materials can improve the electrical conductivity of the composite materials and the Seebeck coefficient can be kept at a stable level or can be improved to some extent. Besides, the thermal conductivity of these composite is still consistent with that of conducting polymers. Therefore, this synthesis effect has provided a new approach to improve the TE properties of conducting polymers. Consequently, we believe that it is greatly significant to investigate the TE performances of PEDOT derivatives and their composeite materials. This dissertation mainly detected and discussed the preparation of PEDOT derivatives/inorganic micro-or nano-composite materials. The major contents and conclusions include:1. We have systematically investigated the thermoelectric performances of PEDOT:PSS films treated with different salts, such as CuCl2or InCl3of different concentration (0.1M and1M). The electrical conductivity, Seebeck coefficient versus temperature are determined, respectively. After treated with aqueous solution of certain salts, the electrical conductivity of PEDOT:PSS films has been improve greatly. The maximum conductivity was up to385.4S/cm at300K, when the films were treated with1M InCl3. While after the treatment, the Seebeck coefficients remain stable and range from11-15.5μA/K, which is in accordance with the pristine PEDOT:PSS film (12.7μV/K). The maximum power factor was up to8.0μW/mK2at300K, and the estimated highest ZT was1.4×10-2.2. Free-standing PEDOT:PSS/Bi2Te3composite films with different Bi2Te3contents were prepared at room temperature by physical mixing, and their TE performance was investigated. The maximum electrical conductivity of the PEDOT:PSS-based polymer composite could reach up to421S/cm, showing a dramatic improvement as compared with pure PEDOT:PSS, while the Seebeck coefficient stayed at a stable level (range of14.2μV/K to18.6μV/K). A relatively high (in the organic TE field) ZT value of0.04was obtained. This study suggests that preparation of polymer-inorganic TE composites is an effective way to improve the thermoelectric properties of conducting polymers and might provide a general concept to improve the TE performance of organic TE materials.3. Layered nanostructure PEDOT:PSS/SWCNTs (single-walled carbon nanotubes) composites have been successfully prepared utilizing a method of two-step spin casting process. SEM, FTIR and Raman were used to analysis the influence of the carbon nanotubes characteristics on the morphological, spectroscopic, electrical and thermoelectric properties. The layered nanostructure composites showed both improved electrical conductivity and Seebeck coefficient as compared to pure PEDOT:PSS. The maximum electrical conductivity and Seebeck coefficient of composites reached241S/cm and38.9μV/K, respectively, and the maximum power factor could be up to21.1μW/mK2, about4orders of magnitude higher than the pure PEDOT:PSS. This study suggests that constructing layered nanostructure organic-inorganic composite might be a novel and effective way for improving the thermoelectric properties of conducting polymers.4. Single-walled carbon nanotubes (SWCNTs) were incorporated with poly(3,4-ethylenedioxythiophene)-block-poly(ethylene glycol) solution (PEDOT-block-PEG) for preparing conducting polymer-based thermoelectric material films by a physical mixing method. Scanning electron microscopy was used to analyze the microstructure of the conductive network nanocomposite films. The maximum electrical conductivity of the nanocomposite could reach up to78.6S/cm, showing a dramatic improvement as compared with pure PEDOT-block-PEG (0.51S/cm at300K). The Seebeck coefficient of the nanocomposite has been enhanced from5.2μV/K to42μV/K. When the content of SWCNTs is66.7wt.%, the maximum power factor was13.9μW/mK2, about3orders of magnitude higher than that of pure PEDOT-block-PEG.The investigation of thermoelectric properties of PSS or PEG modified PEDOT/inorganic micro-or nano-composite materials has indicated that soluble PEDOT based organic/inorganic composite materials will be one of the most potentially thermoelectric materials in the future.