We investigated the structural and thermoelectric properties poly(3,4-ethylenedioxythiophene) (PEDOT) films with several dopants (counter ions, ClO4, PF6, and BF4), synthesised by electropolymerization. We first performed cyclic voltammetry analysis to determine the optimum synthesis conditions of the PEDOT thin films. We found that the surface morphology of the PEDOT thin films was dependent on the type of the dopant. The PF6-doped PEDOT (PEDOT:PF6) thin films showed a dense structure, and the PEDOT:ClO4 thin films showed a highly porous microstructure. Fourier transform infrared (FT-IR) spectroscopy showed that all the PEDOT thin films showed similar chemical structures and the p-type state. Regarding their thermoelectric properties, the electrical conductivity of the all the doped PEDOT thin films increased as the dopant concentration increased, with the PEDOT:PF6 thin films showing the highest value. On the other hand, the Seebeck coefficient of the PEDOT thin films with all the dopants decreased as the dopant concentration increased, with the PEDOT:BF4 thin films achieving the highest value. As a result, the PEDOT:BF4 thin films exhibited the highest power factor of 0.75 µW/(m·K2) at a dopant concentration of 1.0 M. We think that the PEDOT microstructure produced using the different types of dopant may affect the thermoelectric properties.

Effects of ultraviolet (UV) irradiation on ClO4 doped poly(3,4-ethylenedioxythiophene) (PEDOT) thin films were investigated in terms of the structural and thermoelectric properties. The ClO4 doped PEDOT films were synthesized by electropolymerization; subsequently, these films were exposed to UV light for predetermined time intervals in ambient air. UV irradiation led to an agglomeration of PEDOT domains, which in turn causes an increase in the grain size and the surface roughness, as observed in scanning electron microscopy images. Fourier transform infrared spectroscopy revealed that the molecular structure of PEDOT was not affected by UV irradiation. Electron spin resonance (ESR) analysis revealed that the spin density was drastically reduced by short-term UV irradiation of less than 5 min. Upon increasing the UV irradiation time, the spin density gradually increased. A similar relationship was observed between the UV irradiation time and the electrical conductivity. Further, short-term UV irradiation also increased the power factor. The maximum power factor was found to be 1.9 µW/(m·K2) at a UV irradiation time of 2.5 min, this is approximately 60% higher than that of the pristine PEDOT thin film. Therefore, we conclude that the appropriate UV irradiation dosage enhances the thermoelectric performance, but an excess UV irradiation leads to a deterioration of the same.

Continuous Electrodeionization (CEDI) is beginning to be used widely to water treatment systems for the microelectronics, pharmaceutical and power generation industries. The recent microelectronics field requires ultrapure water (UPW) at very low concentration of silica and boron. Whereas, it is difficult to remove such weakly ionized substances up to the required level by conventional CEDI. We have developed a new CEDI, which makes it possible to produce high quality water with silica and boron concentrations below sub ppb level. This paper provides the mechanism of this new technology and performance characteristics of the CEDI module using this technology.

No abstract