Electronic properties, passive layers electron transfer, metallic surfaces

The anodic partial reaction also involves a charge transfer at the interface because a metal atom loses electrons. It then dissolves in the solution as a hydrated or complexed ion and diffuses towards the bulk. In the vicinity of the metal surface, the concentration generated by dissolution therefore often exceeds that of the bulk electrolyte. Once the solubility threshold is reached, solid reaction products begin to precipitate and form a porous film. Alternatively, under certain conditions, metal ions do not dissolve at all but form a thin compact oxide layer, called passive film. The properties of the passive film then determine the rate of corrosion of the underlying metal (Chapter 6). 

Electronic properties can be studied by photoelectrochemistry using redox reactions at passivated metal surfaces in the dark or with illumination. Their knowledge is very valuable to understand layer formation and corrosion phenomena for open circuit conditions, i.e., under the influence of redox systems within the electrolyte. Furthermore layer formation includes often oxidation of intermediates, i.e., oxidation of lower valent to higher valent cations, which requires electronic conduction through the already existing film. Similarly layer reduction needs electron transfer across the film. 

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