The rate-determining step in electrochemical impedance spectroscopy

• The concept of the rate-determining step is introduced into EIS, and discussed for mechanisms with fast mass transport.
• If other steps are much faster than the rds, the impedance spectrum simplifies to a semicircle in the complex plane.
• The capacitance and resistance associated with the semicircle can be related to coverages and kinetics of the rds.

The concept of the rate-determining step (rds) is applied to electrochemical impedance spectroscopy (EIS). For consecutive (sequential) reaction steps with adsorption and fast mass transport, if the rds is preceded by rapid preequilibria and followed by fast steps then the EIS spectrum reduces to a single semicircle in the complex plane. The diameter of this semicircle is the polarization resistance and is related to the kinetics of the rds. The capacitance associated with this semicircle is the sum of the double-layer capacitance and a pseudocapacitance associated with the coverages of species in the preequilibria.

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