Eu2+ and V2+ as electrode kinetic probes of the structure of the diffuse layer in dilute electrolytes

The structure of the diffuse double layer at positive electrode charges in dilute perchlorate, chloride and bromide electrolytes is inferred from the kinetics of oxidation of the Eu²⁺ and V²⁺ cations. Diffuse layer potentials calculated from the measured kinetics disagree, both in magnitude and (in some cases) in sign with potentials calculated from electrocapillary data and Gouy-Chapman-Stern theory. The possible origin of the discrepancies and their consequences in attempts to apply Frumkin double layer corrections or to detect discreteness-of-charge effects are discussed.