What Does Concentration Cell Mean?
A concentration cell is a type of electrolytic cell. What makes a concentration cell different from other electrolytic cells is that rather than having two-half cells with similar or varying compositions and concentrations, a concentration cell has two-half cells with varying concentrations of the same composition.
If concentration cells are allowed to form then corrosion can occur. For instance, if one portion of an object is coated correctly and another portion of that same object is not, the difference in the oxygen concentrations that the object is in contact with can create a difference in electrical potential. This results in the formation of a concentration cell, and ultimately the oxidation of the material.
Corrosionpedia Explains Concentration Cell
A concentration cell will not have varying compositions; it will only have varying concentrations. To further isolate the concentration as the sole variable of a concentration cell, the electrodes in both half-cells of the concentration cell must be the same composition as well. Since the concentrations of the two-half cells are varied, they obviously cannot be stored in the same container. Therefore, a salt bridge is used to connect the two half-cells of the concentration cell and allow for the flow of ions.
A concentration cell will have a difference in electrical potential because of the different solution concentration of the two half-cells. The half-cell with the lesser solution concentration will undergo oxidation. This means that the ions will flow off the electrode and into the solution. The half-cell with the higher solution concentration will undergo reduction, meaning the ions will flow onto the electrode in that half-cell.