## 2 Materials and Methods
### Methods  
For the determination of the thermoelectric properties of the pristine PANI and the PANI-Bi\({}_{0.4}\)Sb\({}_{1.6}\)Te\({}_{3}\) composites, the corresponding powders were processed into pellets using a mechanical press (Manual Hydraulic Press 25 Ton-GS25011, Specac Ltd., Orpington, UK) consisting of a 10 mm diameter cylindrical steel die. The die was encased in a homemade setup that allowed the application of pressure at temperatures up to 150 \({}^{\circ}\)C.  
The effect of various experimental parameters, including processing time, pressure and temperature during pellet formation, along with the percentage of the additive, on the thermoelectric behavior of the produced samples was systematically investigated (Table 1). For the formation of pellets with a diameter of 10 mm consisting of pure PANI, PANI-BST (20 wt.%) and PANI-BST (30 wt.%), the following experimental parameters were employed in the mechanical press:  
* Processing times: 15 min, 45 min and 75 min. * Processing temperatures: 30 \({}^{\circ}\)C, 80 \({}^{\circ}\)C and 100 \({}^{\circ}\)C.
* Processing pressures: 2 tons (250 MPa) and 4.5 tons (562 MPa). \begin{table}
\begin{tabular}{c c c} \hline
**System** & **Model/Manufacturer** & **Accuracy** \\ \hline Measuring Seebeck coefficient and & ZEM-3 (ULVAC) & 5\% \\ electrical conductivity system & NETZSCH LFA 457 & 10\% \\ \hline Process temperatures (\({}^{\circ}\)C) & 30, 80 and 100 & \\ \hline Process pressures (tons) & 2 and 4.5 & \\ \hline Processing times (min) & 15, 45 and 75 & \\ \hline Limitations & Processing with 4.5 tons and 100 \({}^{\circ}\)C & \\ \hline \end{tabular}
\end{table} 
Table 1: Materials characterization systems (models, specifications), processing parameters and limitations of the experimental process. Initially, the powders (PANI and PANI-BST mixtures) were placed in the die and slightly compressed for about 5 min. This was followed by their processing under the desired pressure and temperature for a specific time, as per the aforementioned experimental parameters. Upon the completion of the process, the applied pressure and heating were simultaneously removed. Figure 1 provides a schematic illustration of the experimental process followed in the preparation of the PANI-BST thermoelectric composites. The heat capacity Cp and thermal diffusivity \(\alpha\) of the produced samples were measured using the laser flash technique on a NETZSCH LFA 457 apparatus. For all samples, thermal conductivity was calculated based on this thermal diffusivity and an estimated heat capacity, using a standard pyroceram 9606 as reference. The densities of the produced pellets were estimated based on their dimensions and mass. The Seebeck coefficient and the electrical conductivity were measured using a commercial ZEM-3 (ULVAC) system at a temperature range of 30-150 \({}^{\circ}\)C (303-423 K). Additionally, scanning electron microscopy (SEM, Vega II LSU-Tescan and Jeol JSM-6610 LV) and energy dispersive spectroscopy (EDS, Bruker Quantax 200) analyses were carried out on various samples in order to investigate the morphology and distribution of the inorganic additive within the polymer matrix. Powder XRD was also performed on a composite sample with 30 wt.% BST content using a Rigaku MiniFlex diffractometer (CuK\(\alpha\)-radiation; \(\lambda\) = 0.154 nm), and the X-ray diffractogram is provided in Figure S1 (Supplementary Material). Table 2 summarizes the processing parameters (i.e., processing temperature, pressure and time) applied for the fabrication of pristine PANI and PANI-BST composite pellets with variable BST content, along with the corresponding average density (derived from 2 samples). As seen, the density increases with the increase in BST content. Moreover, a minor increase in density can be observed in the samples prepared upon applying a lower (2 tons) pressure. This can be attributed to the fact that, in the samples that were subjected to 4.5 tons of pressure, more material escaped between the die walls and was hence wasted.