The same reaction occurs in the half-cells but in opposite directions, increasing the lower and decreasing the higher concentration.
This generation of electricity from ambient thermal energy, without a temperature gradient, is possible because the convergence of the chemical concentrations in the two half-cells increases entropy, and this increase more than compensates for the entropy decrease when heat is converted into electrical energy.
Electrolyte Concentration cell - In this particular electrochemical cell, the electrodes within both half-cells consist of identical substances, while the electrolyte comprises a solution of the same substance, albeit with varying concentrations.
In the presence of water, a high concentration of metal ions will exist under faying surfaces and a low concentration of metal ions will exist adjacent to the crevice created by the faying surfaces.
[citation needed] Water in contact with the metal surface will normally contain dissolved oxygen.