Electrochemical Impedance Spectroscopy (EIS)

Electrochemical Impedance Spectroscopy (EIS) is an electrochemical techniques to measure the impedance of a system in dependence of the AC potentials frequency.

This is done by applying a sine-wave potential (AC potential) to the working electrode and read out the current, which should also be a sine wave. With the two sine waves (potential and current) the total impedance and phase shift for the corresponding frequency is calculated.

schematic representation of the potential excitation and current response

Figure 6.1 schematic representation of the potential
excitation and current response in the measurement
setup (left); potential and current waves over time (right)

The data points are either displayed in a Bode plot or used to determine the real and imaginary part of the impedance and presented in a Nyquist plot.

EIS of a Randles circuit including a Warburg element in a schematic Bode and Nyquist plot

Figure 6.8 EIS of a Randles circuit including
a Warburg element in a schematic Bode
and Nyquist plot

By using equivalent circuit fitting the contribution of different effects to the impedance can be calculated. This allows to study changes of the interface in a very sensitive way. EIS is popular for coating research, label-free sensor reseach, or battery studies.

step by step fitting 2

Figure 6.14 Step by Step Fitting part 2