Non-reversible charge transfer and mass transfer: Methodology for experimental characterization without theoretical models

Abstract

Abstract An extension of the methodology based on the concept of mass transfer operator to non-reversible (i.e. quasi-reversible or irreversible) charge transfer is proposed. We show how it is possible to characterize the charge and mass transfer steps, without postulating a modelling equation to describe the behaviour (except a very general assumption of first-order kinetics). The concept of mass transfer operator, which can be written using the convolution formalism, enables us to analyse separately both mass and charge transfer. Using this method, the characteristic parameters of electron transfer can be measured under known mass transport conditions. Conversely, a reverse approach based on the same concepts enables the characterization of any mass transfer associated with the same redox reaction. This new approach proves itself very attractive when no mathematical model is available to describe the electrochemical behaviour of a complex redox system. An example of an application given here is the study under galvanostatic conditions of the Fe ( CN ) 4− 6 Fe ( CN ) 3− 6 redox couple in aqueous solution; our results can be compared with the literature data.