Electrochemically induced ageing of polyaniline monitored by the changes in its voltammetric response

Experimental results for the ageing of polyaniline films of different thicknesses in 3.7 M H2SO4 are presented. The ageing process was monitored by measuring the changes in the voltammetric response. The relation between the changes in the voltammetric peak parameters and the extent of the ageing process is analyzed employing a formal representation of the anodic voltammetric wave. The model considers a contribution of capacitive current together with an electrochemically reversible faradaic process, with interactions between the redox centres. The analysis shows that during the ageing process, only interaction energies between the reduced redox centres change and they become more attractive. Also, it is shown that the extent of the ageing process may adequately be represented by the relative change of the voltammetric peak current. On the other hand, the change of the peak potential is not a direct measure of the extent of the ageing process. It is defined the so-called apparent number of exchanged electrons, nap, which shows the same ageing time dependence as the peak current does. The ageing process is interpreted by an Elovich type of kinetic characterized by a pseudo zero order rate constant, k0, and a parameter, β, that indicates how fast the activation free energy changes with the extent of the process. Values of β and k0 are given for different polymer thicknesses.