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

Abstract

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, HClO 4 and H 2SO 4, and on different piezoelectric quartz crystal (PQC) electrodes, Pt and Au. It is concluded that (1) the PANI film grown on an Au electrode is more stable than that on a Pt electrode; (2) the PANI degradation reaction abides by the zero-order kinetic law in HClO 4 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 H 2SO 4 with rate constants from 2.61×10 −3 to 7.00×10 −3 s −1 on Pt and 1.00×10 −3 to 5.00×10 −3 s −1 on Au at different ion concentrations. The contrary effects of ClO 4 − and SO 4 2− 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.