Electron transfer at surfaces through a blocking layer

4 Electron transfer at surfaces through a blocking layer 

An outer-sphere electron-transfer process should be independent of the nature of the electrode and of the electrolyte medium. Nevertheless, experimental electron-transfer rates are strongly dependent on the electrodes and of their surface history. 

The pre-exponential factor for this electrochemical exchange can be calculated with eq. (16.73) making T = 1. Assuming the monolayer has a refractive index = 1.6, making i i o = 19 A and taking the absolute potential of ferrocene o = 5.17 eV, the frequency factor becomes 10 sec This with the activation free energy already calculated for the Fe(Cp)2° couple, = 21 kJ mol , gives = 0-2 sec at 298 K. It is 

The density of electronic states in the electrode, p, close to the Fermi level of the metal, is dependent on the Fermi energy (Sp), on the number of conducting electrons provided by each atom (AT), and can be estimated within the model of a free electronic gas 

For gold, each atom contributes A = 1 to the electronic gas and Sp = 5.51 eV. Hence the density of states for gold at the Fermi level is p(8p) = 0.27 states eV atom f 

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