Electrochemical impedance spectroscopy (EIS) is one of the most powerful techniques in electrochemical research. The schematic diagram corresponding to this Demonstration is

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The impedance corresponds to the reaction on the surface of the electrode: is the resistance of the solution, is the charge transfer resistance, and is the double layer capacitance. The frequency in electrochemical impedance spectroscopy is normally calculated by the number of frequencies per decade. The Nyquist diagram plots the real versus the imaginary parts of the impedance.