halvcellepotensialmålinger

Half-cell potentials are the electrical potentials of individual electrochemical half-cells measured relative to a reference electrode. In a typical setup, one records the potential of a working electrode as it participates in a redox couple, while a reference electrode provides a stable, known potential against which that value is compared. These potentials are expressed in volts and depend on the chemical environment, including ion concentrations, temperature, and the activity of species in solution.

The concept is central to standard electrode potentials, tabulated as standard reduction potentials E°, usually defined against the standard hydrogen electrode (SHE) at 25°C. Common reference electrodes include the SHE, the saturated calomel electrode, and the silver/silver chloride electrode. The measured half-cell potential can be reported versus SHE or another reference, and it changes with temperature and composition, even when the redox couple remains the same.

The potential of a half-cell is described by the Nernst equation. For a simple redox couple, E = E° − (RT/nF) ln(Q), where Q is the reaction quotient. In practice, this means the observed potential reflects not only the intrinsic tendency of the couple to gain or lose electrons, but also the relative activities (or concentrations) of the oxidized and reduced forms.

In applications such as corrosion science, the open-circuit potential of a metal in a solution is a practical measure of its tendency to oxidize, but it does not alone determine corrosion rate. Interpreting half-cell potentials often requires additional kinetic information, such as Tafel slopes and polarization data.

Examples of standard reduction potentials (vs SHE): Cu2+/Cu ≈ +0.34 V, Ag+/Ag ≈ +0.80 V, and H+/H2 = 0 V.