Überpotentials

Überpotentials, also known as overpotentials, are a phenomenon observed in electrochemistry where the actual potential difference applied to an electrochemical cell is greater than the theoretical equilibrium potential. This excess potential is required to overcome kinetic barriers that prevent the electrochemical reaction from proceeding at an appreciable rate. The term "über" is German for "over" or "excess."

Überpotentials can arise from various sources. These include activation overpotential, which is related to the activation energy required for charge transfer at the electrode surface, and concentration overpotential, which occurs when the concentration of reactants or products at the electrode surface deviates from their bulk values. Ohmic overpotential, sometimes called resistive overpotential, is also a factor, representing the voltage drop across the electrolyte due to its electrical resistance.

The magnitude of the overpotential depends on factors such as the current density, the nature of the electrode material, the composition of the electrolyte, and the presence of impurities or surface modifications. Understanding and minimizing overpotentials is crucial in many electrochemical applications, such as electroplating, electrolysis, and fuel cells, as they directly impact the energy efficiency and reaction rate of these processes. For instance, high overpotentials in electrolysis lead to increased energy consumption.