EFFECTS OF OHMIC RESISTANCE ON THE EVALUATION OF FARADAIC CHARGE IN THIN-FILMS OF REDOX MATERIALS BY IMPEDANCE AND VOLTAMMETRY

It has been reported for a number of systems, such as Ni(OH)(2) or cer tain electronic conducting polymer films, that the charge stored in th e electrode evaluated by ac impedance is significantly lower than that determined by cyclic voltammetry or galvanostatic discharge. The char ges exchanged under low and large amplitude perturbations were investi gated using a staircase potential program. The results obtained with a thin-layer alpha-Ni(OH)(2) electrode were compared with the responses computed from a simple redox model of a two-dimensional interface. Th e calculated data for the profile of the voltammetric peaks, their dep endence on the sweep rate and the transient responses near the peak po tential are in reasonable agreement with experiment. It is concluded t hat the discrepancy observed originates from the non-linearity of the electrode system induced by a sharp transition between the insulating and the conducting states.