The solid metallic electrode some remarks

Mercury is not a typical electrode material it is liquid, and there is constant movement of atoms on the surface in contact with solution. A solid electrode has a well-defined structure, probably polycrystalline and in some cases monocrystalline. In a solid metallic electrode conduction is predominantly electronic owing to the free movement of valence electrons, the energy of the electrons that traverse the interface being that of the Fermi level, EF (Section 3.6), giving rise to effects from the electronic distribution of the atoms in the metallic lattice already mentioned. 

For a metal, the occupation of the electronic levels close to EF is given more correctly by the expression22 

By convention, for a metal, it is said that only electrons with energies within kBT of EF can be transferred. (In the case of semiconductors (3.33) cannot be applied and larger energy intervals have to be considered.) 

The interfacial structure of a solid electrode depends on various factors. The interatomic distance varies with the exposed crystallographic face and with the interaction energy between the crystallites in a polycrystalline material there are breaks in the structure and onedimensional and two-dimensional defects, such as screw dislocations, etc. Adsorption of species can be facilitated or made more difficult, and at the macroscopic level we observe the average behaviour. 

The effects of the crystallographic face and the difference between metals are evidence of the incorrectness of the classical representations of the interface with all the potential decay within the solution (Fig. 3.13a). In fact a discontinuity is physically improbable and experimental evidence mentioned above confirms that it is incorrect, the schematic representation of Fig. 3.136 being more correct. This corresponds to the chemical models (Section 3.3) and reflects the fact that the electrons from the solid penetrate a tiny distance into the solution (due to wave properties of the electron). In this treatment the Galvani (or inner electric) potential, (p, (associated with EF) and the Volta (or outer electric) potential, ip, that is the potential outside the electrode s electronic distribution (approximately at the IHP, 10 5cm from the surface) are distinguished from each other. The difference between these potentials is the surface potential x (see Fig. 3.14 and Section 4.6). 

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