Kinetics and mechanism of the electrochemical p-doping of PEDOT

EQCM experiments were made on PEDOT films exposed to LiClO₄/CH₃CN under permselective conditions and subjected to cyclic voltammetry in the potential range corresponding to p-doping. Current and frequency responses were used to generate time-resolved ion and solvent flux data as functions of potential. These fluxes normalize with respect to scan rate during p-doping and undoping, but the responses in the two directions are not mirror images. The results lead to the following mechanistic conclusions. Coupled electron/anion transfer is the first, and non-rate limiting, step in both redox switching directions, but involves differently solvated and configured polymer in the two directions. Solvent transfer and polymer reconfiguration follow the charge transfer steps, but are kinetically inseparable on the timescales accessed. This mechanism can be visualized by a scheme-of-squares representation whose two coordinates are "coupled electron/anion transfer" and "coupled solvent transfer/polymer reconfiguration". The data analysis protocol provides a powerful approach to identifying mechanistic pathways, particularly in situations corresponding to partial film redox conversion.