Metal Deposition is an Unexpectedly Fast Reaction

The deposition of a metal is a charge transfer reaction, just like an outer-sphere charge transfer reaction, at least it would appear to be, when the reactions are written side by side, for example, 

But in spite of the apparent similarity, the two reactions represent very different physical situations, and they are expected to follow different mechanisms. 

Metal deposition involves the transfer of mass across the interface, while for outer-sphere charge transfer to occur only electrons have to cross the interface, while both the reactant and the product stay on the solution side of the compact Helmholtz double layer. 

Based on the above differences, one would expect outer-sphere charge-transfer reactions to be many orders of magnitude faster than metal deposition. Surprisingly, such a trend is not observed experimentally. The heterogeneous rate constant for the two reactions shown in Eq. (19.17) and Eq. (19.18) are = 2.0 and 0.9 cm s respectively. Even the rate of deposition of trivalent bismuth, having a very high 

What Carries the Charge Across the Inter ce During Metal Deposition  

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