An easy method for calculating kinetic parameters of electrochemical mechanisms: Temkin’s formalism

In this educational article the formalism developed by Temkin for a consecutive chemical mechanism is applied to work out the kinetic laws of consecutive electrochemical reaction mechanisms. The benefits of this approach will be highlighted in comparison with classical treatments such as the Quasi Equilibrium and the Steady State approximations. In particular, the use of this formalism becomes even more advantageous when the number of reaction steps increases. Introduction One of the typical problems addressed in electrochemical textbooks is how to define the theoretical kinetic law of an electrochemical reaction and how to propose a plausible mechanism for this reaction from its kinetic parameters, usually the Tafel slope and reaction orders. Most electrochemical reactions consist of at least two electron transfers and it is usually accepted that their probability of being multiple simultaneous electron transfers is low, i.e. only single electron transfer reactions are possible (although it seems that simultaneous two electron transfer can occur in certain cases). Thus, for an n-electron transfer reaction such as R Ox ne + ƒ several mechanisms with different rate determining steps, rds, and different intermediates are possible. The simplest two electron homogeneous redox process is composed of two single electron transfer steps and two diffusion steps, the diffusion of the reactant from the bulk solution to the electrode surface and the diffusion of the product from the electrode