The Potentiostatic EIS techniques are used to characterize an electrochemical interface which is held at a fixed potential. A small-amplitude AC-voltage excitation is applied to an electrochemical cell. The phase-sensitive AC response of the interface is measured as the frequency of the excitation signal is varied.

EIS is a particularly powerful tool for the study of coated-metal corrosion. It is also useful in almost every other area of electrochemistry, including research in batteries, electrode kinetics, and industrial electrolysis.

The output of an EIS experiment is a complex impedance spectrum. The term *complex i*s used in its mathematical sense: containing both real and imaginary terms. An EIS spectrum is usually graphed as either a Bode plot (impedance magnitude and phase plotted versus frequency) or a Nyquist plot (imaginary impedance plotted versus real impedance). Analysis of the impedance spectrum can give you the following information:

- Polarization resistance
- Double-layer capacitance
- Solution resistance
- Coating-defect parameters
- Mechanistic and kinetic information

The Potentiostatic OptiEIS technique applies the same principle as a potentiostatic EIS scan, but the signal is a collection of multiple frequencies combined into a unified signal. The complex response-pattern can be deconstructed via FFT to resolve the impedance spectra. The techniqueâ€™s major advantage is a large reduction in experimentation time for the sub-millihertz and below frequency range.