NON-REVERSIBLE CHARGE-TRANSFER AND MASS-TRANSFER - METHODOLOGY FOR EXPERIMENTAL CHARACTERIZATION WITHOUT THEORETICAL-MODELS

An extension of the methodology based on the concept of mass transfer operator to non-reversible (i.e. quasi-reversible or irreversible) cha rge transfer is proposed. We show how it is possible to characterize t he charge and mass transfer steps, without postulating a modelling equ ation to describe the behaviour (except a very general assumption of f irst-order kinetics). The concept of mass transfer operator, which can be written using the convolution formalism, enables us to analyse sep arately both mass and charge transfer. Using this method, the characte ristic parameters of electron transfer can be measured under known mas s transport conditions. Conversely, a reverse approach based on the sa me concepts enables the characterization of any mass transfer associat ed with the same redox reaction. This new approach proves itself very attractive when no mathematical model is available to describe the ele ctrochemical behaviour of a complex redox system. An example of an app lication given here is the study under galvanostatic conditions of the Fe(CN)(6)(4-)/Fe(CN)(6)(3-) redox couple in aqueous solution; our res ults can be compared with the literature data.