# One-Dimensional Nanostructure Engineering of Conducting Polymers for Thermoelectric Applications
## 2 D-Conducting Polymers and Their Thermoelectric Properties
### Pedot  
PEDOT is the most widely investigated conducting polymer for thermoelectric application due to a high electrical conductivity when mixed with the respective additives or dopants, low thermal conductivity and a relatively large Seebeck coefficient upon appropriate treatment and optimization [21; 22; 23]. Moreover, PEDOT-based materials possess significant advantages, such as material abundance, superior optical transparency, solution processability, good physical and chemical stability, providing an opportunity for large-scale fabrication of flexible and printed thermoelectric devices. In the past few years, the synthesis and investigation of nanostructured PEDOT for different applications are gaining increasing research interest [32; 33; 34; 35; 36; 37; 38; 39]. In 2011, [PERSON] et al. first investigated the thermoelectric properties of PEDOT nanowires, which were synthesized by oxidative electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer in aqueous LiClO\({}_{4}\) solution via a hard template through a lithographically patterned nanowire electrodeposition (LPNE) approach with non-dependent control over the thickness and width of the nanowire (Figure 1) [34]. These PEDOT nanowire arrays (40-90 nm thick, 150-580 nm wide and 200 \(\upmu\)m long) exhibit much higher Seebeck coefficient (\(-122\)\(\upmu\)V K\({}^{-1}\) at 310 K) compared to bulk PEDOT films (\(-57\)\(\upmu\)V K\({}^{-1}\) at 310 K). Moreover, the electron mobility of the prepared PEDOT nanowires is two times higher than that of the films, which is in accordance with the better electrical conductivity of the nanowires (40.5 S cm\({}^{-1}\) versus 18.3 S cm\({}^{-1}\) (films) at 310 K). The greatly enhanced thermoelectric properties are attributed to the orderly arrangement of the PEDOT chains and the crystalline structure of PEDOT within the nanowires. Using the hard-template method, [PERSON] et al. recently reported a three-dimensional (3D) assembly of PEDOT nanowires synthesized by electrochemical polymerization in 3D-alumina templates [39]. A free-standing network was attained after removal of the template. Two types of PEDOT nanowires (C-PEDOT and T-PEDOT) were generated by using different oxidants, FeCl\({}_{3}\) and Fe(Tos)\({}_{3}\), respectively. These two types of nanowires possess a similar average diameter of 12 nm, but with different lengths (0.5-5 \(\upmu\)m for C-PEDOT and 0.2-0.7 nm for T-PEDOT), as shown in the TEM images (Figure 2a,b). The C-PEDOT nanowires, which consist of much longer polymer chains and higher molecular weights, exhibit an extremely high electrical conductivity of 540 S cm\({}^{-1}\) and an enhanced Seebeck coefficient, which is 2.6 times that of the PEDOT: poly(styrenesulfonate) (PSS) films. After hydrazine treatment, the 3D network can reach an optimum power factor of 35.8 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\), which is the highest ever reported amongst all of the reported 1D conduc  
Figure 1: (**a**) Schematic synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) nanowire arrays using the lithographically patterned nanowire electrodeposition (LPNE) process. (**b**) Bright field optical micrograph of PEDOT nanowire pattered on glass. (**c**) Atomic force microscope (AFM) image of an array of 40 \(\times\) 200 nm PEDOT nanowires on glass. A height versus distance trace across these nanowires is shown at bottom. (**d**) Measured Seebeck coefficient versus nanowire height for PEDOT nanowires and films at 310 K. (**e**) Electron mobilities versus the film or nanowire height, showing also (horizontal line) the mean mobility value. Readapted with permission from American Chemical Society [34]. In 2015, [PERSON] et al. reported the thermoelectric performance of nanostructured PEDOT with various morphologies (Figure 3a-e) by chemical oxidation polymerization in reverse microemulsions with sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as the surfactant [35].