Influence of the Faradaic Process on Nonfaradaic Resistance Compensation in Potentiostatic Techniques

The theoretical justification for the use of IR compensation in potentiostatic techniques when a faradaic reaction is present is considered in detail. It is shown that the stability of the system indeed depends on potentiostat and all electrode parameters, i.e., both the double layer and faradaic time constants contribute. Under certain conditions, the faradaic contribution is not significant; however, it is difficult to determine even in an a posteriori manner the remaining uncompensated resistance Ru. It is concluded that IR compensation can only be employed unambiguously in the time and classical a-c frequency domains if the critical damping frequency is accurately known and the frequencies employed are sufficiently lower than this frequency. IR compensation can however be advantageously employed in combination with the transient impedance technique over the entire accessible frequency range (even those above τmin) and which allows the system to be unmasked experimentally from the effects of nonfaradaic resistance. This permits the necessary kinetic and double-layer information to be extracted from the final results with a precision increased at least two orders of magnitude above the uncompensated system when high-speed circuitry is employed.