Ecorr

Ecorr, short for corrosion potential, is the electrode potential of a metal in an electrolyte at which the anodic and cathodic current densities are equal, resulting in zero net current. It is typically measured relative to a reference electrode such as Ag/AgCl, saturated calomel electrode (SCE), or the standard hydrogen electrode (SHE).

In practice, Ecorr is obtained from open-circuit potential measurements conducted during exposure to the electrolyte, or inferred from potentiodynamic polarization curves by extrapolating the linear portions of the anodic and cathodic branches to their intersection. The current density at this intersection is denoted i_corr and represents the corrosion current density.

Ecorr is highly environment-dependent. It varies with electrolyte composition, pH, temperature, surface condition, alloying elements, and the presence of protective films or inhibitors. It is not an intrinsic property of the metal alone, and it can drift over time as surfaces passivate or films form and dissolve. Moreover, Ecorr does not by itself quantify corrosion rate; i_corr or polarization resistance are typically used to estimate that rate. A higher (more noble) Ecorr does not guarantee lower corrosion risk if the environment promotes rapid anodic dissolution or if protective films fail.

Applications of Ecorr include comparing materials or coatings in the same environment and assessing galvanic interactions when multiple metals are coupled. It serves as a reference point in corrosion testing and materials selection, while recognizing its dependence on testing conditions.