Dynamiques des systèmes - Impédances électrochimiques (System dynamics - Electrochemical impedances)

Electrochemical impedance spectroscopy (EIS) technique is introduced for characterizing electrochemical systems based on the application of a low amplitude sinusoidal signal to the electrochemical system and measuring its response at different frequencies. When applied to the corrosion of metallic materials, the test is based on the application of a low alternating potential at the input, by means of a reference electrode (RE) and a platinum counter electrode (CE) connected to a potentiostat. Measuring the output current, between the CE electrode and the working electrode (WE), which will allow the impedance (alternating current resistance) to be calculated. The equations involved are explained to help researchers better understand the technique. Several cases are presented. In order to be able to measure an output current, it is necessary that the product – the electrolyte – has a minimum conductivity. This measurement is carried out at different frequencies during the test, typically between 10 mHz and 100 kHz. The physical model used to quantify the response of the coating to the product, the electrolyte, is an RLC model: resistance, induction, capacitance.