Linear sweep voltammetry. Effect of uncompensated cell resistance and double layer charging on polarization curves

Abstract

Summary Ohmic drop in the uncompensated cell resistance influences simultaneously the double layer charging current and the faradic current. Consequently, the effect of the ohmic drop on the polarization curves depends not only on the magnitude of the uncompensated cell resistance, but also on the diffeential capacity of the double layer. Theoretical relations have been derived that related the peak characteristics to these quentities as well as to the other experimental factors (sweep rate, depolarizer concentration, etc.) through two adimensional independent parameters. The theoretical analysis is devoted to the case of a Nernstian charge transfer, kinetic control being by diffusion. The double layer capacity is assumed to be constant and independent of the course of the faradaic process in the potential range considered. It is shown that evaluation of the ohmic drop effect on the peak can be significantly erroeous, especially at high sweep rates, if the influence of the double layer charging is ignored. A series of experiments have been performed with the system fluorenone-fluorenone anion in acetonitrile. The results are used to test the validity of the theoretical analysis and to exemplify the orders of magnitude of the ohmic drop effects in the current practice of linear sweep voltammetry. A simple correction procedure is suggested for small values of the ohmic drop.