Diffusion layer

The Nernst diffusion layer is the area between cathode and electrolyte in which mass transport is only possible by diffusion.

The “thicker” the diffusion layer, the longer the distance the ions have to travel in this way, the lower the concentration balance of dischargeable ions between the electrolyte and the cathode surface. It follows that the thickness of the diffusion layer has a direct influence on the maximum applicable current density (limiting current density).

The thickness of the diffusion layer increases with increasing current density and decreases with increasing temperature and relative motion.