Electrochemical Fabrication And Properties Of PEDOT:PSS Electrode Based Conducting Polymer Thermoelectric Materials

Energy is indispensible for industrial production and daily life. Currently, as the world’s increasing demand for energy and serious environmental problems, exploring environmentally friendly energy becomes one of the important approaches to keep sustainable development of the economy and society. Thermoelectric (TE) material is a kind of functional material that can directly realize the conversion of electrical energy and thermal energy, and cooling and power generation system based on TE materials can realize the recycling of waste heat. Compared with inorganic materials, organic TE materials inherently possess numerous advantages of light quality, good flexibility, easy processing, abundant resources, and especially low, thermal conductivity. Recently, conducting polymer TE researches have gradually become the hot spots.Electrochemical polymerization is one of the important methods to prepare conducting polymers, with several merits of one-step film formation, small amounts of monomer, and controlled reaction rate. It is well known that electrochemical polymerization depends strongly on many variables, and the electrode is one of the most critical. Traditional electrodes such as platinum and indium tin oxide (ITO) possess the defects of high price and shortage of resources. Hence, it is of great importance to explore new electrode materials. Poly(3,4-ethylenedioxythiophene): polystyrenesulfonate (PEDOT:PSS) is the most widely applied conducting polymer, and its electrical conductivity can be effectively enhanced by secondary doping, which is beneficial for the applications of organic electronic devices such as solar cells and light-emitting diodes. In theory, multilayered nanostructures can change the electronic density of states near the Fermi level, leading to the improvement of electrical conductivity. In this work, PEDOT:PSS nanofilm has firstly been used as working electrode to electrodeposite other conducting polymers in different electrolyte, fabricating a series of multilayered conducting polymer nanofilms, and the TE performance has been systematically investigated. The major contents and conclusions are as follows:1. PEDOT:PSS nanofilm has been used as working electrode to electrodeposite thiophene and its derivatives of 3-methylthiophene and 3-hexylthiophene in boron trifluoride ethyl ether (BFEE) system, fabricating PEDOT:PSS/polythiophenes bilayered nanofilms with good electrochemical stability, and cross-section SEM images show obvious layered structures. TE results indicates that the electrical conductivity of the films is enhanced, due to the high conductivity of PEDOT:PSS layer, with the electrical conductivity of 123.9,136.5, and 200.5 S cm-1 for PEDOT:PSS/PTh, PEDOT:PSS/P3MeT, and PEDOT:PSS/P3HT. The maximum power factor is 5.79 μW m-1 K-2 for the case of PEDOT:PSS/P3HT. Thus, it may provide a general strategy for fabricating conducting polymer TE materials.2. PEDOT:PSS nanofilm has been used as working electrode to electrodeposite 1,12-bis(carbazolyl)dodecane in dichloromethane (CH2Cl2) and BFEE system, fabricating PEDOT:PSS/poly(1,12-bis(carbazolyl)dodecane) (P2Cz-D) bilayered nanofilms. The influence of BFEE content (5～50%) on TE performance is carefully investigated, and the results suggest that the maximum electrical conductivity of PEDOT:PSS/P2Cz-D can reach up to 41.2 S cm-1 when the BFEE content is 20%, which is six orders of magnitude higher than that of P2Cz-D films, and the power factor is 0.23 μWm-1 K-2.3. PEDOT:PSS nanofilm has been used as working electrode to electrodeposite pyrrole and aniline in isopropyl alcohol (IPA), BFEE, and polyethylene glycol (PEG) system, fabricating PEDOT:PSS/polypyrrole (PPY) and PEDOT:PSS/polyaniline (PANI) bilayered nanofilms with good electrochemical stability. The influence of BFEE content (10～30%) on TE performance is carefully investigated, and the results suggest that the electrical conductivity increases with the increase of BFEE content, with the maximum values of 97.1 and 212.6 S cm-1 for PEDOT:PSS/PPY and PEDOT:PSS/PANI. It is encouraging that the Seebeck coefficient is also enhanced, with the maximum values of 23.3 and 27.8 μV K-1. The maximum power factor is 12.0 μW m-1 K-2 for PEDOT:PSS/PANI, obtaining the ZT value of 2.12×10-2 by estimates.4. Single-walled carbon nanotubes (SWCNTs)/PEDOT:PSS nanofilm has been used as working electrode to electrodeposite pyrrole and aniline in IPA, BFEE, and PEG system, fabricating SWCNTs/PEDOT:PSS/PANI bilayered nanofilms. At the same time, SWCNTs and PEDOT:PSS/SWCNTs electrodes have been used for comparison. TE measurement shows that the electronic conductivity of SWCNTs/PEDOT:PSS/PANI is larger than that of SWCNTs/PANI and PEDOT:PSS/SWCNTs/PANI, with the value of 232.0 S cm-1, and the Seebeck coefficient is 23.0 μV K-1, making the power factor reach up to be 12.3μW m-1 K-2.