First-Order ECirre Mechanism Basic Concepts

First-Order ECirre Mechanism Basic Concepts 

The first reaction mechanism we are going to consider is the ECjrre mechanism, where E refers to a heterogeneous electron transfer reaction and Cirre to an irreversible chemical reaction in solution. The ECirre case enables 

Considering the scheme (5.1), the problem includes three imknowns the concentrations of species A, B and Y that each depend on both time and distance to the electrode surface. The concentration of species A in solution is only subject to transport by diffusion such that its variation with time and distance is described by Pick s second law thus, for linear diffusion. 

Note that this does not mean that the concentration profile of species A is equivalent to that of the E mechanism since it will be influenced by the chemical reaction through the surface boundary conditions. Thus, the chemical reaction affects the surface concentration of species B, which is related to that of species A through the Nernst equation (for reversible systems), or more generally, through the Butler-Volmer or Marcus-Hush relationships. Therefore, the surface concentration of species A, and as a consequence the whole concentration profile, will reflect the presence of the chemical process. 

Regarding species B and Y, their concentrations will undertake diffu-sional and chemical changes simultaneously. Accordingly, an additional term associated with the conversion of species B into Y appears in the continuity equations 

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First-Order ECirre Mechanism Basic Concepts... 

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