Preparation And Thermoelectric Properties Of PEDOT:PSS/SWCNT Composite Fibers

With the rapid development of wearable electronics in areas such as the Internet of Things,soft robotics,and healthcare devices,the development of high-performance flexible thermoelectric materials has become the focus of current thermoelectric research.The one-dimensional structure of PEDOT:PSS thermoelectric fibers combines good wear resistance and shape adaptation,making them highly desirable for flexible wearable electronic device applications.However,directly prepared PEDOT:PSS fibers usually have poor thermoelectric properties and cannot meet the application requirements of wearable devices.It has been shown that PEDOT:PSS compounded with carbon-based nanomaterials is one of the key and effective methods to develop high-performance thermoelectric materials.Based on this,in this work,single-walled carbon nanotubes（SWCNTs）and PEDOT:PSS were formed into composite materials,and PEDOT:PSS/SWCNT composite thermoelectric fibers were prepared by wet spinning.The influence of parameters such as solidification bath type,soaking time,and pinhole size on the fiber microstructure was explored.The morphology and structure of fiber was optimized by ionic liquid adding and base treatment to improve its thermoelectric properties.The specific studies are as follows:1)The PEDOT:PSS/SWCNT/IL composite fiber was prepared by adding ionic liquid1-Ethyl-3-methylimidazolium trifluoromethanesulfonate（IL）to the composite system and using isopropyl（IPA）as the coagulation bath by wet spinning method.The results showed that the PEDOT:PSS/SWCNT/IL composite fibers with 10 wt%IL has an electrical conductivity of 1540 S cm^-1,a Seebeck coefficient of 30.6μV K^-1,and a power factor of 145μW m^-1 K^-2 at room temperature,which was further increased to 236μW m^-1 K^-2 by optimizing the treatment time of concentrated H2SO4.The analysis revealed that IL can promote the phase separation of PEDOT from PSS and facilitate the formation of linear quinone-type conformation of PEDOT.Meanwhile,the specific interaction of imidazole ions in IL withπ-electron nanotube surface facilitates the depolymerization and dispersion of carbon nanotubes.H2SO4 post-treatment further removes the PSS chains,which in turn enhances the electrical conductivity and thermoelectric properties.2)Continuous and highly conductive PEDOT:PSS/SWCNT composite fibers were prepared by direct wet-spinning of PEDOT:PSS/SWCNT dispersions using sulfuric acid（H2SO4）as the coagulation bath,and the thermoelectric properties of PEDOT:PSS/SWCNT composite fibers were further improved with Na OH post-treatment.The results showed that the primary spun PEDOT:PSS/SWCNT composite fiber had a conductivity of 2982 S cm^-1,a Seebeck coefficient of 27.1μV K^-1,and a power factor of 219μW m^-1 K^-2 at room temperature.The modified power factor was further increased to 280μW m^-1 K^-2 by controlling the concentration and time of Na OH treatment.The analysis revealed that concentrated H2SO4 as coagulation bath could directly remove part of the insulating PSS chains during the spinning process and significantly enhance the conductivity.The Na OH treatment led to partial de-doping of PEDOT:PSS,which effectively reduced the carrier concentration and promoted the increase of Seebeck coefficient,and finally synergistically enhanced the thermoelectric properties of the fiber.The flexible thermoelectric generator based on this fiber has a high output power（0.41 n W）at 10 K temperature difference,demonstrating its potential application in the field of wearable thermoelectrics.