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Concentration polarization

Concentration polarization, only forms on cathodic electrode? or may diffuse on anodic electrode?

Leila Abkar
- Tehran, Iran
2006

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2006

Anything that interferes with a desired electrochemical process or discourages it from proceeding may go by the name of "polarization". One thing that may happen at a cathode is that the boundary layer may interfere with the smooth and rapid movement of ions from the bulk of the solution to the metal surface. In that case, metal ions that have made it through are quickly plated out, and the result is that the concentration of metal ions in the solution right at the metal interface is lower than in the bulk of the solution. That is an impediment to the plating and it is called concentration polarization.

But sometimes the language can get in the way instead of helping to clarify something. While anodes can certainly "polarize", I'm not so confident that the previously described concentration polarization exists on anodes. That would mean that a localized deficiency of anions at the surface of the anode exists because of the boundary layer, and that lack of ions is slowing the dissolution of the anode? Or would it mean that there is an excess of anions right at the anode surface because they can't diffuse through the boundary layer quick enough. If either of those two scenarios was a reality with an actual effect on plating speed, I guess it could be called anodic concentration polarization.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey