Tafelpolarisaatio

Tafelpolarisaatio, also known as Tafel polarization or Tafel extrapolation, is a concept in electrochemistry used to study the kinetics of electrode reactions. It describes the linear relationship observed between the logarithm of the current density and the overpotential for an electrochemical reaction, once the overpotential is sufficiently large. This relationship is known as the Tafel equation.

The Tafel equation is typically expressed as η = a + b log(j), where η is the overpotential, j is the current density, and a and b are constants. The constant 'b' is particularly important as it is directly related to the charge transfer coefficient and the number of electrons transferred in the rate-determining step of the electrochemical reaction. By plotting the logarithm of current density against the overpotential and observing a linear region, researchers can determine the Tafel slope and extrapolate it back to the equilibrium potential to estimate exchange current densities, which are a measure of the intrinsic rate of the electrochemical reaction at equilibrium.

Tafel polarization is a valuable tool for understanding reaction mechanisms, determining rate constants, and evaluating the performance of electrochemical systems such as batteries, fuel cells, and corrosion processes. It allows for the separation of activation overpotential from other forms of overpotential, providing insights into the fundamental kinetics of electron transfer at an electrode surface. The deviation from linearity at lower overpotentials is often attributed to other kinetic or mass transport limitations.