A comparative study on polyaniline degradation by an electrochemical quartz crystal impedance system: electrode and solution effects

By combining the piezoelectric quartz crystal impedance (PQCI) and electrochemical impedance spectroscopy (EIS) measurements, we conducted a comparative study on polyaniline (PANI) degradation in different media, HClO4 and H2SO4, and on different piezoelectric quartz crystal (PQC) electrodes, Pt and An. It is concluded that (1) the PANI film grown on an An electrode is more stable than that on a Pt electrode; (2) the PANI degradation reaction abides by the zero-order kinetic law in HClO4 with rate constants from 0.17 to 2.25 Hz s(-1) on Pt and 0.16 to 0.83 Hz s(-1) on Au, but the first-order kinetic law in H2SO4 With rate constants front 2.61 x 10(-3) to 7.00 x 10(-3) s(-1) on Pt and 1.00 x 10(-3) to 5.00 x 10(-3) s(-1) on An at different ion concentrations. The contrary effects of ClO4- and SO42- on PANI degradation may be understood from the Hofmeister series of anions; (3) the dissolution of the PANI film bulk, the increase of film porosity and the film attenuation occurred simultaneously during degradation via systematic analyses of the motional resistance (R-1)and electrochemical impedance spectra responses, etc. (C) 2003 Elsevier B.V. All rights reserved.