## 1 Introduction
The four-electrode method has been frequently used to overcome the interference that occurs at the electrode-skin interface, while the method with two-electrodes presents the advantage that it does not require a circuit as complicated as that for measuring the impedance by the four-electrode method [14]. For ECG monitoring, used to detect cardiovascular disease, the bioimpedance electrodes are positioned on the chest, neck, finger or wrist [15]. A category of polarizable electrodes is the orbital electrodes. Dry polarizable orbital electrodes are made to last longer than the common clinical electrodes such as Ag/AgCl. An orbital electrode consists in a mixture of metals like aluminium, gold/gold chloride nickel and titanium and stainless steel. They can cause skin irritation over long-duration use [16,17]. In the last period, the polymers are the most promising organic materials for electronic applications, as stretchable electronic skin and flexible biomedical sensors, due to their valuable properties, like good mechanical deformability and robustness, higher device density, and skin biocompatibility. The polymers can replace the metallic electrodes, which are stiff and uncomfortable for the skin [10,12,18]. Elastomers represent the first class of polymers with applications in bioimpedance electrodes for ECG monitoring, for example, PDMS (polydimethylsiloxane). [PERSON], [PERSON] et al. developed a flexible dry sensor on polyethylene terephthalate PET substrate. A silver electrode was printed was deposited on this PET substrate by the screen printing method. Finally, it was deposited on the printed Ag electrode the composite multi-walled carbon nanotubes (MWCNT)/PDMS, by using a bar coating technique. However, the electrodes presented high impedance values and good linearity of impedance-frequency curve [19,20]. [PERSON] et al. developed a flexible dry sensor for ECG monitoring by depositing gold on PDMS films using a plasma treatment; however, this sensor presents a poor skin-contact electric connectivity [21]. Recently, different conductive polymers, such as polythiophene, polyaniline, and polypyrrole(PPY), are used in various fields like flexible electronic devices, sensors, catalysis, batteries, supercapacitors, microactuators, anti-electrostatic coatings, low-cost solar cells, and biomedical, due to their excellent electrical conductivity, thermal stability, environmental stability and relative ease of synthesis. These good properties come from their chemical structure, e.g., conjugated electrons or alternating the single bond with a double bond system [22; 23; 24; 25; 26]. A conductive polymer used as a bioimpedance electrode can be the composite PEDOT/PSS, poly (3,4-ethylenedioxythiophene):(styrenesulfonic acid), where PSS is used as a doping agent. [PERSON], [PERSON] et al. developed a bioimpedance sensor based on PEDOT/PSS, with low impedance, over conventional material such as gold, which is due to the low charge transfer resistance of PEDOT/PSS [27]. [PERSON], [PERSON] et al. developed a bioimpedance sensor based on PEDOT/PSS coated on a fabric characterised by low impedance and long-term stability. However, making the sensor is complex and expensive and presents a poor linearity of the impedance-frequency curve [28]. This polymer was used to achieve the electrode patterns on textiles because it presents a low impedance contact with human skin. From the conductive polymers, the polypyrrole was the most studied, experimented and used in various applications because of its good electrical and electronic properties, good stability derived from its aromatic ring chemical structure, and \(\pi\)-conjugated bonds, which can be modified by oxidation and protonation [29; 30].