Electrochemical and Mass Change Study of the Growth of Poly-(o-Phenylenediamine) Films on Au Substrates

The electropolymerization of o-Phenylenediamine (oPDA), both in the absence and presence of Fe3+ in solution, was investigated in detail using cyclic voltammetry concurrently with the quartz crystal microbalance (QCMB) technique. It is shown that a set of redox peaks (A1/C1), seen between 0.05 and 0.4 V is characteristic of the phenazine-like PoPDA polymer, produced by the irreversible radical oxidation of the oPDA monomer at a Au surface and forming an oPDA radical cation that initiates the polymerization step at >0.8 V vs. RHE. The QCMB results showed that ca. 20% of the oxidized product deposits on the Au surface as a redox-active polymer film, with charge compensation by H+ injection/expulsion along with some inhalation/exhalation of water. The presence of Fe3+ in solution during electropolymerization led to very similar electrochemistry, with ca. 50% of the oxidized product forming the redox-active polymer film. The PoPDA films are very smooth and uniform, while films formed in the presence of Fe3+ are coated with Fe-containing nodules ca. 0.8 μm in diameter, which hinder the further growth of the PoPDA film.