The influence of uncompensated solution resistance on the determination of standard electrochemical rate constants by cyclic voltammetry, and some comparisons with a.c. voltammetry

Abstract

a digital simulation analysis is presented of the deleterious effects of uncompensated solution resistance, R us, on the evaluation of standard rate constant, k s ob, by cyclic voltammetry. The results are expressed in terms of systematic deviations of “apparent measured” rate constants, k s ob(app), evaluated in the conventional manner without regard for R us, from the corresponding actual values, k s ob(true), as a function of R us and other experimental parameters. Attention is focused on the effects of altering the electrode area and the double-layer capacitance on the extent of the deviations between k s ob(app) and k s ob(true), and on comparisons with corresponding simulated results obtained from phase-selective a.c. impedance data. The extent to which k s ob(app) < k s ob(true) for small R us values was found to be similar for the cyclic and a.c. voltammetric techniques. The latter method is, however, regarded as being preferable under most circumstances in view of the greater ease of minimising, as well as evaluating, R us for a.c. impedance measurements. The influence of solution resistance on k s ob measurements with microelectrodes and without iR compensation is also considered.