Ylipotentiaali

Ylipotentiaali, meaning "overpotential" in Finnish, refers to the excess voltage required to drive an electrochemical reaction at a given rate, beyond its thermodynamic equilibrium potential. This phenomenon arises from kinetic barriers within the electrochemical process, such as the activation energy needed for charge transfer at the electrode surface or for mass transport of reactants to and products away from the electrode.

Different types of overpotential contribute to the overall phenomenon. Activation overpotential is associated with the slow kinetics of electron transfer reactions at the electrode-electrolyte interface. Concentration overpotential is caused by the depletion or accumulation of reacting species at the electrode surface, leading to concentration gradients that hinder the reaction rate. Sometimes, ohmic overpotential, due to the resistance of the electrolyte or the electrodes themselves, is also considered, though it is more a voltage drop than a kinetic barrier.

Understanding and minimizing overpotential is crucial in various electrochemical applications. In batteries and fuel cells, high overpotentials lead to reduced efficiency and power output. In electrolysis, increased overpotential translates to higher energy consumption. Research in electrochemistry often focuses on developing electrocatalysts that can lower the activation energy of reactions, thereby reducing overpotential and improving the performance of electrochemical devices. The magnitude of overpotential is dependent on factors such as electrode material, electrolyte composition, temperature, and current density.