Contact adsorption shifts the redox electron level

2 Contact adsorption shifts the redox electron level. 

The kinetic treatment for the electron transfer of ligand-coordinated redox particles described in Sec. 8.4.1 may, in principal, apply also to the electron transfer of adsorbed redox particles (inner-sphere electron transfer). The contact adsorption of redox particles on metal electrodes requires the dehydration of hydrated redox particles and hence inevitably shifts the standard Fermi level of redox electrons from in the hydrated state to in the adsorbed state. This shift of the Fermi level of redox electrons due to the contact adsorption of redox particles is expressed in Eqn. 8-83 similarly to Eqn. 8-79 for the complexation of redox particles (ligand coordination)  

Further, the contact adsorption may reduce the reorganization energy, ) , of redox particles in electron transfer the distribution of electron levels of adsorbed redox particles may be narrower than that of simply hydrated redox particles as shown in Fig. 8-36. Furthermore, the contact adsorption of redox particles produces (1) an increase in the effective cross section for electron capture due to the overlapping of the frontier oihital of adsorbed particles with the band orbital of 

On account of these effects, the contact adsorption of redox particles frequently accelerates the redox electron transfer, as compared with the direct electron transfer between the hydrated redox particle and the electrode. In other words, the reaction current due to redox electron transfer will be greater with adsorbed redox particles than with simply hydrated redox particles if the contact adsorption shifts the energy level of redox electrons in the favorable direction. 

Note that the redox reaction of electron transfer via adsorption intermediates requires the adsorption and desorption processes to occur as the preceding and 

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