WarburgImpedanz

WarburgImpedanz, also known as the Warburg impedance, is a concept in electrochemistry that describes the impedance observed in systems where the diffusion of a reactant to an electrode surface is the rate-limiting step. This phenomenon is particularly relevant in electrochemical impedance spectroscopy (EIS) measurements. The Warburg impedance arises from the concentration gradients that form near the electrode surface as the electrochemical reaction proceeds. As ions or molecules diffuse to replenish the consumed species, they encounter resistance, leading to an increase in impedance with decreasing frequency.

Mathematically, the Warburg impedance is inversely proportional to the square root of the angular frequency and is dependent on the diffusion coefficient of the electroactive species and the concentration of the species. At low frequencies, diffusion is slow and becomes a significant limitation, resulting in a higher impedance. Conversely, at high frequencies, the reactant has ample time to reach the electrode surface, and diffusion is not rate-limiting, leading to a lower impedance. The Warburg impedance is often represented as a straight line with a slope of -0.5 on a log-log plot of impedance magnitude versus frequency, or a phase angle of -45 degrees. Understanding the Warburg impedance is crucial for analyzing electrochemical processes, characterizing mass transport limitations, and determining diffusion coefficients in various electrochemical systems.