ELECTROCHEMICAL AND MASS MEASUREMENTS DURING SMALL VOLTAGE AMPLITUDE PERTURBATIONS OF CONDUCTING POLYANILINE FILMS

The electrochemistry of conducting polyaniline (PANI) films has been s tudied in sulfuric acid solutions using a.c. impedance and cyclic volt ammetry (CV), coupled with the quartz crystal microbalance (QCMB) tech nique. In normal full potential range slow sweep CV experiments, the f act that the mass-to-charge ratio increases markedly with potential in the positive scan, but is essentially constant during the negative sc an, may be related to slow water penetration into the film during its oxidation. When only small potential amplitudes of ca. 25 mV or less a re employed, the CV and QCMB measurements reveal that additional film sites can be initially oxidized, but not reduced, unless the potential is made more negative. This leads to an apparent loss in film capacit ance when only narrow potential ranges are cycled. These results, toge ther with increased hysteresis in the mass response with increasing sw eep rate as well as the known asymmetries of the PANI CV response, sug gest that given enough time, water can penetrate the film, hydrating s ome of the reduced PANI sites and facilitating their oxidation but not their reduction. The subsequent steady-state but lowered film capacit ance must reflect the reversible oxidation/reduction of film sites whi ch are not susceptible to delayed water transport and/or the stabilizi ng effects due to site hydration. (C) 1998 Elsevier Science S.A.