Impedance Spectroscopy is the study of the change in total impedance with changing frequency. It is used to study how different components of a circuit change and how they are related to each other. Impedance spectra are plotted using two types of plots: Bode plots and Nyquist plots. Bode plots depict changes in impedance and phase angle as a function of frequency. They also show the relationship between the real and imaginary components of the total impedance.

## Current relaxation after a voltage step

The use of impedance spectroscopy has increased tremendously in biotechnology. The electrodes used are typically modified by physical or chemical coupling with biofunctional molecules, aggregates, and lipid/protein membranes. In this way, it is possible to detect and measure adsorption processes. Impedance spectroscopy can be performed in two different time domains: the frequency domain and the time domain.

In impedance spectroscopy, the current relaxation after a voltage step is a result of the change in amplitude in the system’s impedance. This relaxation results in the impedance spectrum taking on the shape of a semi-circle.

## Nyquist plots

When using Nyquist plots in Impedence Spectroscopy, it’s important to remember that they are scaled according to the impedance. The larger the impedance, the more scaled the plot will be. Otherwise, it will be difficult to identify the low-impedance semicircle.

Real systems have far more complex impedance than the one shown in Figure 2. The likelihood of finding a perfect semicircle on a Nyquist plot is very low, which is why the most common method of fitting the data is equivalent circuit modelling (ECM). This involves a complex nonlinear least-squares (CNLS) fit to the experimental data. It requires specialized software and good starting values.

## Bode plots

In impedance spectroscopy, Bode plots are plots of the impedance spectrum. These plots are based on the concept of the Nyquist plot. In this plot, the real and imaginary parts of the impedance are plotted. Each point represents a specific frequency.

Bode plots are used to plot the response of an electrochemical system. They are also used to determine the polarization resistance of a system. In these plots, the real part of the impedance is plotted on the x-axis and the imaginary part on the y-axis. To understand a Bode plot, we need to consider how the impedance changes with frequency.

## Electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool in electrochemical research. It can be used to interrogate materials and full cell devices to analyze the behavior of individual components. This review describes recent developments in EIS for solid-state electrolytes and discusses how it can be applied in electrochemical research.

Typically, this method involves calculating the impedance of a sample of a substance by comparing the resistance of its constituent components. These results are used to evaluate the performance of electrochemical systems. In electrochemical impedance spectroscopy, impedance is measured in ohm square metres and is commonly expressed as ohms per square metre.