# One-Dimensional Nanostructure Engineering of Conducting Polymers for Thermoelectric Applications
## 3 Strategies to form 1D Conducting Polymer Nanocomposite Thermoelectric Materials
### Self-Assembly of 1D Conducting Polymer with Nanofilers  
Very recently, [PERSON] et al. reported a new type of thermoelectric composite film by self-assembly of PEDOT nanowires with tellurium nanowires (Figure 13) [101]. The PEDOT nanowires (with an average diameter of 12.2 nm and length of 1.2 um) were synthesized by oxidation polymerization of ethylenedioxythiophene (EDOT) monomer using SDS as cylindrical soft template and FeCl\({}_{3}\) as oxidant and further doped with 5% dimethyl sulfoxide to improve the dispensability. The PEDOT nanowire suspensions were physically mixed with various fractions of Te nanowires (with average diameter of 40 nm and length of 3 um) and subjected to vacuum filtering to afford the PEDOT nanowire/Te nanowire composite films. When Te nanowires were added, the thermoelectric power factor of the composites improved by \(\sim\)40%. When increasing the Te nanowire content from 0 to 95 wt%, the Seebeck coefficient rose from 20.18 to 28.46 uV K\({}^{-1}\), and the electrical conductivity dropped from 541  
Figure 12: (**a**) Schematic comparison of preparation of P3 HT/DWCNT nanocomposites through simple blending and covalent grafting. Reaction route for the synthesis of (**b**) P3 HT-NH\({}_{2}\) and (**c**) P3 HT-g-DWCNT. (**d**) Seebeck coefficient (red column), electrical conductivity (blue column), and corresponding power factor (green column); (**e**) thermal conductivity, and (**f**) figure of merit of pristine DWCNT, P3 HT-g-DWCNT, and physically mixed P3 HT/DWCNT nanocomposites. Readapted with permission from Elsevier Ltd. [100].  
to 38.76 S cm\({}^{-1}\). The maximum PF of 29.05 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\) was achieved with 30 wt% Te nanowire content, which is significantly greater than the respective components (22 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\) for PEDOT nanowires, 1.28 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\) for Te nanowires). The thermoelectric performance enhancement could be attributed to the large carrier mobility in nanowire composites and proper energy barrier at polymer/inorganic boundary.  
In addition to PEDOT, 1D nanostructured PPy has also been reported to form self-assembled hybrid thermoelectric materials with carbonaceous nanofillers. [PERSON] et al. have prepared free-standing PPy nanotube/reduced graphene oxide (rGO) composite films with good mechanical strength and flexibility through vacuum filtration of a blend of GO nanosheets and solution-prepared PPy nanotubes, followed by hydrogen iodide (HI) reduction (Figure 14a,b) [102]. The PPy naontubes were homogeneously intercalated into the rGO nanolayers, which effectively prevent the agglomeration of rGO nanosheets and provide sufficient conducting pathways for charge transfer. The power factor of the PPy/rGO composite film can reach up to 7.28 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\) at room temperature, which is 135 times that of the pure PPy film. [PERSON] et al. also reported self-assembled composite films from PPy nanowires and SWCNTs (Figure 14c,d) [103]. The PPy nanowires prepared by chemical oxidative polymerization were physically mixed with CNTs and subjected to vacuum filtration to afford the free-standing hybrid films. A classic layered structure made up of parallel CNT nanosheets in between PPy nanowires with a diameter of 55-75 nm was obtained. The hybrid films exhibit outstanding thermoelectric performance with optimum power factor up to 21.7 \(\pm\) 0.8 \(\upmu\)W m\({}^{-1}\) K\({}^{-2}\), which outperforms other PPy-based composites reported thus far.  
Figure 13: (**a**) Schematic illustration of the fabrication process of the Te nanowire/PEDOT nanowire composite films. (**b**) Measured thermoelectric properties including S, \(\sigma\) and PF of the composites relative to the mass fraction of Te nanowires. (**c**) SEM image of the surface morphology of 70 wt% Te nanowire/PEDOT nanowire composite films. Readapted with permission from American Chemical Society [101].