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Experimental results for the ageing of polyaniline films of different thicknesses in 3.7 M H2SO4 are pre- 22polyaniline films of different thicknesses in 3.7 M H2SO4 are pre- 22 sented. The ageing process was monitored by measuring the changes in the voltammetric response. The 2323 relation between the changes in the voltammetric peak parameters and the extent of the ageing process 2424 is analyzed employing a formal representation of the anodic voltammetric wave. The model considers a 2525 contribution of capacitive current together with an electrochemically reversible faradaic process, with 2626 interactions between the redox centres. The analysis shows that during the ageing process, only interac- 2727 tion energies between the reduced redox centres change and they become more attractive. Also, it is 2828 shown that the extent of the ageing process may adequately be represented by the relative change of 2929 the voltammetric peak current. On the other hand, the change of the peak potential is not a direct mea- 3030 sure of the extent of the ageing process. It is defined the so-called apparent number of exchanged elec- 3131 trons, nap, which shows the same ageing time dependence as the peak current does. The ageing process is 32nap, which shows the same ageing time dependence as the peak current does. The ageing process is 32 interpreted by an Elovich type of kinetic characterized by a pseudo zero order rate constant, k0, and a 33pseudo zero order rate constant, k0, and a 33 parameter, b, that indicates how fast the activation free energy changes with the extent of the process. 34b, that indicates how fast the activation free energy changes with the extent of the process. 34 Values of b and k0 are given for different polymer thicknesses.b and k0 are given for different polymer thicknesses.