Polyaniline films of different thickness were formed on Pt and Au electrodes. In-situ epr spectra at different applied potentials in various pH media were reported in order to clarify the conducting mechanism. The results indicate that upon electrochemical doping of polyaniline, an equilibrium between polaron and bipolaron occurs. The thicker the film, the more stable the polaron. The more acidic the medium , the more stable the polaron. The stability of the polaron of polyaniline formed on Pt is better than those formed on Au electrode. A small epr spin density maximum appear before the major spin density maximum on the plot of spin density versus applied potential of polyaniline formed on Pt electrode. This phenomenon may result from polarons in different environments.
