The coulostatic impulse technique: a critical review of its features and possibilities

Abstract

Characteristics features of the charge impulse relaxation technique are reconsidered. Together with a discussion on the definition of coulostatic pulses, fundamental differences with comparable relaxation techniques are pointed out. The usual experimental arrangements are discussed and some possibilities for a simple check on reliability are suggested. The influence of double layer relaxation effects on the coulostatic response is treated extensively, starting from recent work on the mechanism of charging ionic double layers. These effects appear to be absent from coulostatic overvoltages in the μs range if the (1–1) electrolyte concentration in the (aqueous) solution is not less than 0.005 M. Analysis of coulostatic relaxation curves normally starts with a log η vs time plot and it is calculated the exchange current densities up to about 0.1 A cm −2 can be evaluated within 10% inaccuracy. In the case of fast electrode processes, Laplace transformation of the experimental data followed by complex plane analysis, is recommended. This procedure enhances the limit of applicability by about a factor of 10. Finally, some typical categories of experiments are indicated where the coulostatic technique is especially attractive: kinetic, double layer and analytical measurements in poorly conductive systems, kinetic and double layer measurements in systems where fast interfacial processes can take place or where electrochemical parameters are time-dependent.