Randles

Randles is a surname and a term encountered in electrochemistry, where it names a standard circuit model used to interpret electrochemical impedance spectroscopy data. The Randles circuit is a simple equivalent electrical circuit that represents the impedance of a polarized electrode in an electrolyte.

The typical Randles circuit consists of a solution resistance Rs in series with a parallel network of charge-transfer resistance Rct and double-layer capacitance Cdl, together with a Warburg element Zw that accounts for diffusion. A common formulation for the total impedance is Z(ω) = Rs + [ (Rct || 1/(jωCdl)) + Zw(ω) ], where j is the imaginary unit and ω is angular frequency. The Warburg element models semi-infinite diffusion and introduces a characteristic 1/√ω dependence at low frequencies.

In impedance spectra, the Randles circuit produces a semicircular arc at moderate frequencies due to Rct and Cdl, with diffusion effects represented by the Warburg tail appearing at low frequencies. It remains a widely used baseline model for interpreting data from batteries, corrosion studies, fuel cells, and electroplating processes. By fitting experimental spectra to the Randles model, researchers estimate the charge-transfer resistance, double-layer capacitance, and diffusion parameters, aiding in the assessment of electrode kinetics and mass transport.

As a surname, Randles is found in English-speaking regions and may be borne by individuals across various professions. In science and engineering contexts, the term Randles frequently refers to the associated electrochemical circuit model rather than to a person.