Principle : In addition to the technical stationary (usually relations current-voltage) that allow us to study the electrochemical processes the most simple, the techniques of non-stationary are needed to analyze systems electrochemical more complex. the use of these last is based on principles similar to those which justify the employment of relaxation methods in chemical kinetics at equilibrium. a disturbance of the electrochemical system moves the reactions of their steady state. as the various elementary processes change at different speeds, the system response can be analyzed to dissect the electrochemical process overall.
among the techniques that non-stationary, the techniques of impedance are increasingly used in electrochemistry as well as for academic studies and for industrial applications to characterize the processes at the electrodes. this technique is based on the analysis of the current response (in potential) to a disturbance of low amplitude, often sinusoidal, the potential (or current). the measurement is to bias potential constant, as soon as the interface has reached a steady state, by varying the frequency of analysis in a wide field of frequencies (often of 50 khz to 0.001 hz). it then repeats this measurement all along the curve of current-voltage in the area of potential studied.