LIMITING CURRENT DENSITY2

"The mass transport occurs exclusively through diffusion in the diffusion layer, driven by the concentration difference of the reactant between the edge of the diffusion layer and the electrode surface. As the current density is increased (usually by changing the electrode potential), the surface concentration of the reactant must decrease so that the concentration difference driving the diffusion can increase and provide the required flux of the reactant. However, the surface concentration obviously cannot decrease below zero, thereby a situation is reached when further change of the electrode potential cannot increase the reactant flux, and correspondingly the current density. The concept of ""limiting current density"" is valid even in the absence of supporting electrolyte. However, the situation is more complex in this case because electromigrational effects must also be taken into consideration. "