elektrodenpotentiaal

Elektrodenpotentiaal, or electrode potential, is the electric potential difference between an electrode and its surrounding electrolyte when the electrochemical interface is at equilibrium. It arises from the interfacial electric double layer and specific adsorption of species at the electrode surface, and it reflects the thermodynamics of the redox couple while depending on ion activities, temperature, and the structure of the interface. Each electrode in a cell has its own potential; the absolute value is defined only relative to a reference electrode.

Standard electrode potential (E°) is the potential of a redox couple measured under standardized conditions (298 K, unit activities) relative to the standard hydrogen electrode. The sign indicates the tendency to gain or lose electrons; positive E° denotes a tendency to be reduced. Examples: Cu2+/Cu ≈ +0.34 V; Zn2+/Zn ≈ −0.76 V versus SHE. Measurement uses a reference electrode and a potentiometric instrument. The Nernst equation relates electrode potential to the activities of the redox species: E = E° − (RT/nF) ln Q. At 25°C this simplifies to E = E° − (0.05916/n) log Q. For a simple couple, Q is the ratio of activities of products to reactants.

In a galvanic cell, the overall cell potential Ecell equals the difference between the electrode potentials: Ecell = Ecathode − Eanode. Electrode potentials can deviate from their equilibrium values under non-ideal conditions due to kinetic overpotentials, concentration polarization, and mass transport limitations. Applications include predicting reaction spontaneity, designing batteries and fuel cells, corrosion protection, electroplating, and electrochemical sensing. Common reference electrodes are Ag/AgCl and saturated calomel; the standard hydrogen electrode remains the reference for defining E°.