Effect of electrode morphology on the diffusion length of the doping process of electronically conducting polypyrrole films

We report on a correlation between ionic diffusivity and electrode morphology of polypyrrole films. The film thickness (polymerization charge) modifies the diffusion characteristic frequency extracted using capacitance plots, which varies heavily from 1 to 100 mHz. A transition between two types of deposition mechanisms from nuclei growth at initial polymerization stages (thinner, more regular layers) to 1-D transversal growth after nuclei overlapping (thicker, porous structures), explains the change of behavior of the diffusion characteristic frequency observed at Q approximate to 60 mC cm(-2). Changes of film structure were also observed by scanning electron microscopy. The value of diffusion characteristic frequency measured at initial deposition stages indicates that the chemical diffusion coefficient D similar to 10(-11) cm(2) s(-1). Other thermodynamic parameters such as specific equilibrium capacitance and diffusion resistance were also determined. (C) 2003 Elsevier Science B.V. All rights reserved.