Ennobling the Metal Surface

The ennobling of the metal surface is based on the assumption that the conducting polymer, in its oxidized state, will set the metal at a potential within its passive range where the dissolution rate is slow. This generally involves the formation of a thin insulating metallic oxide layer, more or less porous, the effect of which is to protect the metal from a rapid dissolution, and make it behave like a noble metal. To understand this effect it must be recalled that three distinct areas related to active, passive, and transpassive 

Nevertheless, when a conducting polymer in its oxidized state is coated on the metal, there is galvanic coupling between the metal and the polymer. The corrosion current has a kinetic origin and corresponds to a mixed potential resulting from the reduction of the 

However, as previously described, this ennobling mechanism is only based upon steady-state considerations, and it does not adequately take into account electrochemical kinetics, which, depending on the experimental conditions (polymer, substrate, aeration of the environment... [41]), makes the protection efficiency vary considerably. 

Similar experiments using various electrolytes and, in particular, known passivating anions have also been reported. Such experiments are useful for rationalizing the so-called ennobling effects. 

A significant improvement of the ennobling effect was also observed when the PPy fdm on the ring was replaced by a composite film (PDAN/PANI) [59]. However, as previously, the ohmic drop between the bare metal and the eoated area resulting from the slow corrosion impeded the repassivation of the exposed metal, and resulted in the disappearance of the ennobling effect. 

---

The paints must exhibit metallic properties to ennoble the metal surface. 

---