Effect of the potential on the electrochemically induced ageing of polyaniline films

Abstract

The electrochemically induced ageing of polyaniline films, as a function of the ageing potential, was investigated employing films of different thicknesses in 3.7 M H2SO4 solutions. The ageing process was monitored by the change of the voltammetric response in a subsequent positive going potential scan after the ageing. It is observed that the ageing process, at more positive potentials, involves increasing amounts of non-reduced polymer. Also, it is observed that the rate of ageing decreases as the ageing potential increases. The changes in the voltammetric response after ageing is interpreted through a model for the voltammetric response, previously developed, that includes capacitive currents and interactions between the redox centers. The analysis shows that neither the capacitive parameters nor the total faradaic charge change during the ageing. On the other hand, only the interaction energy between the reduced centers change during the ageing. This fact leads to a narrowing of the formal redox potential distribution that can be characterized by the apparent number of exchanged electrons. The decrease of the interaction energy between reduced centers is consistent with the reduction of the free energy of the polymer during the ageing. The kinetics of ageing is analyzed through an Elovich type of equation from which k0, the pseudo zero order rate constant and β, a parameter that indicates how fast the activation free energy changes with the extent of the process, can be obtained. © 2012 Elsevier B.V. All rights reserved.