The resistance to over-oxidation for polyaniline initiated by the resulting quinone-like molecules

Polyaniline (PANI) suffers electrochemical over-oxidation at high anodic potentials, which leads to severe degradation, forming quinone-like molecules (hydroquinone/benzoquinone, HQ/BQ). A research area usually neglected is the influence of the newly-produced HQ/BQ on the over-oxidation of PANI. In this study, it has been examined by cyclic voltammetry (CV) and FT-IR spectroscopy. When HQ was intentionally added into sulfuric acid solutions, the cyclic voltammograms demonstrate that the rate of degradation turned to be lower as the concentration of introduced HQ increased. First-order rate constants obtained from kinetic study were shown to vary between 0.1399 and 0.1027 s⁻¹ within the concentration range of HQ from 0 to 0.05 M. An important finding is that the quinone-like molecules may have a great electronic exchange with the nitrogen atoms of the intact PANI chain when adsorbed on it, which leads to the changes in PANI structure at the molecule level. Less pernigraniline (PEB) was finally obtained and thus slower degradation was observed. This conclusion is supported by the phenomenon that the peak potentials for emeraldine/pernigraniline (EM/PEB) transitions shifted to more positive values when HQ was added. Moreover, from FT-IR analyses, it seemed that the relative content of the reduced form of PANI ascended with the degradation. So, the existence of HQ/BQ enhances the stability of PANI structure, endows PANI with resistance to over-oxidation and protects it from further degradation to a certain extent.