Application of the superposition principle to the study of multistep electrode processes and systems with several components in chronopotentiometry with programmed current. I (Q1381260)

From the point of view of both electrochemistry and chemical kinetics, the study of electrode processes in which oxidation or reduction reactions take place in several steps is of great interest. Thus, for example, fullerenes in general and \(\text{C}_{60}\) in particular can present up to five reversible one electron reductions. The theoretical study of electrode processes that involve several successive steps in electrochemical techniques with controlled current is a very old one. However, papers which tackled these processes when a determined current is applied to an electrode have only considered the case of planar diffusion. Yet plane electrodes are not the most suitable for the study of such processes owning to their poorly reproducible surface which tends to accumulate contamination on the electrode-solution interface. More suitable, as is well known, are those electrodes of spherical geometry, such as the dropping mercury electrode (DME) and the static mercury electrode (SMDE), which show a clean, perfectly reproducible and contamination-free surface. Moreover, by using a time-variable current in this last type of electrodes, it is possible to eliminate most of the double layer effects if we work with not very high concentrations of electroactive species and/or small electrode radii. The main aim of this paper is to find a general analytical expression for the response of this type of electrode processes in chronopotentiometry with a programmed current. This technique consists of applying a current that is a known function of time through a function generator. Due to the fact that in chronopotentiometry the response obtained (potential-time curve) is a function of the concentrations of species participating in the surface of the electrode, it is possible, by determining the analytical expressions for these concentrations, to characterize the process thermodynamically and kinetically by analysis of the variation of the potential over time. We have also deduced the expression corresponding to the response obtained for the system of several components whose deduction turns out to be much simpler than that corresponding to multistep processes.