Question

Why metal deposition occurs at potentials negative of nernst potential?

Answer 1

University of Leuven

If You talk about electro depositing (or electroplating) of metals out of a solution then look at the ionic form :Me+(++) witch means that the metal ions are charged positive. They are attracted towards the negative electrode where they should be reduced to Me thus catching an electron from the electrode. In the ideal case the reduced metal ions will form a coherent metal film. For cleaning we want to remove the outer layer of the metal electrode. Applying a positive potential will cause the surface to 'oxidize so the metal will form ions witch go into solution ( the opposite process) leaving a clean surface. About the cleaning: often the generation of gas on the electrode is also used as cleaning technique ( hydrogen at the cathode or oxygen at the anode. There are some risks involved like inclusion of Hydrogen witch can lead to embrittlement .

In all these cases we talk about two electrodes in a solution having a potential difference or tension over them. An other way to describe this is using the halve cells with there Nernst potentials