Medelpotential

Medelpotential, often referred to in English as mixed potential, is a concept in electrochemistry describing the electrode potential that arises at a surface where multiple redox reactions occur and no net current flows. It represents the balance point at which the competing anodic and cathodic processes neutralize each other, rather than a potential set by a single redox couple.

Mechanism and theory: Each electrochemical reaction on a surface has a polarization curve that relates current density to potential. Anodic processes (such as metal dissolution) contribute positive current, while cathodic processes (such as reduction of dissolved species) contribute negative current. The net current is the sum of these contributions. The medelpotential is the potential at which this total current is zero, meaning the magnitude of the anodic current equals the magnitude of the cathodic current. The exact value depends on the kinetics of the involved reactions, concentrations of reacting species, temperature, and the surface state. In corrosion science, the mixed potential concept helps explain why a metal in a corrosive environment exhibits a potential that reflects the balance of several redox couples rather than a single couple.

Applications and scope: Medelpotential is used to interpret open-circuit potentials of metals in electrolytes, assess corrosion risk, and analyze electrode behavior in sensors and electrocatalysis. It informs strategies to control corrosion or tailor catalytic activity by influencing the relative rates of competing reactions, for example through alloying, inhibitors, or surface treatment.

Limitations: The model assumes distinct, separable reactions with well-defined kinetics and a relatively uniform surface. In systems with strong coupling, diffusion limitations, or significant surface heterogeneity, the simple balance may not accurately describe the observed potential.