absolutepotential

Absolute potential, often referred to in electrochemistry as the absolute electrode potential (AEP), is a theoretical construct that assigns an electrode a potential energy reference with respect to the vacuum level. It provides a universal energy scale for comparing the electrochemical potential of different materials, independent of the solvent, ion environment, or chosen reference electrode used in a measurement.

In practice, potentials in electrochemistry are measured as differences between electrodes, so an absolute value cannot be observed directly. AEPs are therefore anchored to reference scales such as the standard hydrogen electrode (SHE) or to the vacuum level through thermodynamic data and computational models. In solid-state contexts, the AEP is related to the work function and the Fermi level relative to vacuum; the work function is the energy required to remove an electron from the Fermi level to the vacuum, a concept closely tied to AEP discussions.

Applications of the concept include interpretation of photoelectrochemical processes, charging of electrode/electrolyte interfaces, and the comparison of catalytic or corrosion behavior across different materials. AEP-based reasoning helps unify disparate measurements by providing a common energetic reference, even though the actual observable quantities are potentials or voltages measured between two electrodes.

Limitations arise because the vacuum level at an interface is not directly measurable in situ, and surface states, adsorbates, and solvent effects can shift the reference. Consequently, AEPs are typically inferred values, used to aid comparison and modeling rather than as directly observable quantities.