ABSTRACT
These considerations between current and electrode potential were obtained from thermodynamic principles. In fact, the amount of current crossing the working electrode | solution interface is a measure of the kinetics of the redox reaction, which can be broken down into three steps, as shown in Figure 7.2:
• flux of the solution reactants towards the electrode (diffusion-migration) • interfacial electron transfer reaction
• flux of the products from the surface towards the solution (diffusion-migration)
It is customary to recognise three cases:
• The mass transfer, diffusion/migration flux of the reactants and the products of the electrode reaction, is rapid compared with the electron transfer reaction. The reaction is said to be ‘irreversible’. This expression has nothing to do with the chemical reversibility of the reaction, which indicates whether the reaction can happen in both directions, but indicates simply in electrochemical jargon that the limiting slow step for the reaction is the electron transfer reaction at the electrode. Note also that the notion of electrochemical reversibility also has no relation to thermodynamic reversibility.
