Impedance study of the charge-transfer interaction between the polyanilinechain and redox pair in solution

The impedance method was used to study the charge-transfer interaction betw een the polymer conducting chain (emeraldine form of polyaniline, PANI) and active molecules in solution (tetrafluorohydroquinone, 4F-Hqui). Equivalen t electrical circuits were found for steady-state potentials of the PANI el ectrode and their parameters were analyzed as dependent on pH. In the prese nce of 4F-Hqui in the pH range -0.3 to 3, active molecules appear in the do uble electrical layer and alter the charge exchange between electrode and s olution (extrinsic reaction) and faradaic charging of PANI (intrinsic proce ss). Charge-transfer (CT) resistance increases with respect to acid-only so lutions; nevertheless, conductivity through the polymer still limits electr ical transport at low frequencies. In low pH solutions the protonated imine centers of PANI interact with hydroquinone molecules forming H bonds along the polymer chain. We have proposed that such a structure could serve as a n electron path in the moment of the charge transfer. When pH is increased above seven, the CT complex decomposes irreversibly, the polymer electrode is modified and loses its conductivity. We have proposed and discussed poss ible chemical structures for the modified polymer, its acid transformation, and electrochemical doping. (C) 2000 The Electrochemical Society. S0013-46 51(99)11-032-2. All rights reserved.