A MICROELECTRODE STUDY OF THE INFLUENCE OF PH AND SOLUTION COMPOSITION ON THE ELECTROCHEMICAL-BEHAVIOR OF POLYANILINE FILMS

Platinum microelectrodes (diameter 10-mu-m) have been used to study the influence of pH, ionic strength, isotopic substitution and different anions on the redox switching of electrochemically prepared polyaniline (PANI) films under first cycle and multicycle conditions. Microelectrodes reduce iR errors greatly and allow rapid scan cyclic voltammetry (greater-than-or-equal-to 100 V/s) to be used in order to avoid degradation of the PANI in the region of the second oxidation peak. In all cases, the oxidation charge passed on the first cycle was found to be larger than on subsequent cycles (the first cycle effect). The multicycle switching charge was found to decrease with increasing pH, decreasing ionic strength and with increasing anion size, whereas the charge associated with the first positive scan was much less affected. More positive oxidation peaks were also obtained in DCl and D2SO4 than in HCl and H2SO4, respectively. It is concluded that the oxidation of PANI proceeds initially via rapid field driven proton egress, followed by equilibration of the oxidised phase by diffusion controlled movement of acid. Under multicycle conditions, part of the oxidized PANI film appears to remain inactive, but can be reduced if the potential is held at -0.2 V vs. SCE for several minutes. The loss of electroactivity under reduction conditions suggests that ion ingress is much more difficult than ion egress in the PANI system.