Kinetic Influence of Adsorption

When considering how the adsorption of different snbstances on electrodes inflnences the kinetics of electrochemical reactions, we mnst distingnish two cases that where components are adsorbed which are involved in the reaction, and that where incidental snbstances are adsorbed which are not involved in the reaction. 

mnltistep reactions are enconntered where a reactant j first becomes adsorbed on the electrode, then is converted electrochemically (or chemically) to a desorbing prodnct. We shall consider the case where the electrochemical step involving adsorbed particles is rate determining. With a homogeneons electrode surface and without interaction forces between the adsorbed particles [i.e., in conditions when the Langmuir isotherm (10.14) can be apphed], the assumption can be made that the rate of this step is proportional not to the bulk concentration Cy j but to the surface concentration Aj or to the degree of surface coverage 0 hence. 

However, with an inhomogeneous electrode surface and adsorption energies that are different at different sites, the reaction rate constant and the related parameter will also assume different values for different sites. In this case the idea that the reaction rate might be proportional to surface concentration is no longer correct. It was shown by M. Temkin that when the logarithmic adsorption isotherm (10.15) is obeyed, the reaction rate will be an exponential function of the degree of surface coverage by the reactant  

Substituting into this equation the expression for 9 from the isotherm equation, we find that 

In a number of cases, electrochemical reactions involving adsorbed substances exhibit special kinetic features. For instance, when the reactant bulk concentration is 

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