The impedance response of rotating disk electrodes

• Comprehensive review of models for rotating disk electrode.
• Explanation for origin of complex ohmic impedance.
• Explanation for frequency dispersion caused by disk geometry.
• Explanation for frequency dispersion caused by coupling of faradaic and charging currents.

Classifications and recent findings are reviewed for numerical simulations describing the impedance response of rotating disk electrodes. The disk geometry is shown to cause a complex character to the ohmic contribution to the impedance response. For reactions that do not involve formation of adsorbed intermediates, the frequency dispersion associated with the disk geometry occurs above a characteristic frequency. Such dispersion may be avoided by selecting a disk of sufficiently small dimension. For reactions that do involve formation of adsorbed intermediates, a low-frequency dispersion is also seen. Models including the influence of mass transfer show that the coupling of faradaic and charging currents induces frequency dispersion at frequencies associated with the faradaic reaction.