Mechanism of underpotential deposition of metal on conducting polymers

From the idea of underpotential deposition (UPD), the electrochemically depositing and dissolving processes of copper (Cu) onto and from polypyrrole (PPy) were investigated. A mechanism was proposed to illustrate the whole metallization process. The results indicate that two forms of coppers, valence and elemental ones, can be formed on PPy at a constant cathodic potential. However, only the valence Cu can be left on PPy at the anodic stripping. From the X-ray photoelectron spectroscopy (XPS) and surface-enhanced Raman scattering (SERS) analyses, it is found that the valence Cu is interacted with the pyrrolylium nitrogen, resulting from an electron transfer from the Cu atom to the PPy nitrogen. The effect of the deposition methods of Cu onto PPy on its corresponding property was also discussed.