Concentration Polarization
A visual explanation of oxygen depletion near the steel surface and why potentials shift more negative.
What you’re seeing: Oxygen is plentiful in the bulk electrolyte, but oxygen becomes scarce right at the steel surface. When oxygen near the steel is depleted, the cathodic reaction slows and the measured potential must shift more negative to keep the reaction moving.
How to read this graphic
- Left side (Bulk Electrolyte): oxygen is abundant and evenly available throughout the electrolyte.
- Right side (Concentration Polarization): oxygen is still present away from the surface, but depleted near the steel.
- Key idea: the limiting factor is oxygen reaching the steel surface—not electrons traveling through the steel.
- Field impact: potentials can shift more negative when oxygen at the surface is limited.