Characteristics of the polyaniline anodic pre-peak

A detailed study of the origin and meaning of the anodic pre-peak, A(0), wa s carried out for polyaniline (PANI) films, which were electrochemically gr own using the potential sweep method to two different upper potential limit s (Type I and Type IT films) on Au, Pt and GC electrodes. The observed pres ence of a matching cathodic peak, C-0, for slowly grown Type I films, and t he absence of the A(0) pre-peak for rapidly formed Type II films, suggest t hat the pre-peak arises from the oxidation of particular PANT sites within these films, likely located near the underlying substrate. Time of cycling over the A(0)/C-0 potential range (0 and 0.3 V) and/or holding of the poten tial in the reduced film state causes the A(0) peak potential to shift. Sim ultaneous cyclic voltammetry, quartz crystal microbalance and ellipsometry measurements indicate that the positive movement of the A(0) potential is r elated to film swelling. Long times of cycling between 0 and 0.6 V appear t o cause the Type I film to anneal, resulting in a more compact PANI film, a nd a negative shift of the pre-peak. The pre-peak, therefore, appears to be a barometer of film water and/or solution anion content. (C) 1999 Elsevier Science Ltd. All rights reserved.