AC impedance method is a very important method in electrochemical testing technology, which is an important means of studying electrode process dynamics and surface phenomena. Especially in recent years, due to the rapid development of frequency response analyzers, the testing accuracy of AC impedance has become higher and higher, and the impedance spectrum of ultra-low frequency signals has good reproducibility. In addition, with the advancement of computer technology, the automation of impedance spectrum analysis has become higher and higher. This enables us to better understand the double layer structure of electrode surfaces, activate passivation film conversion, induce, develop, terminate pore corrosion, and the adsorption and desorption process of active substances.
1. Basic components in impedance spectrum
The analysis of AC impedance spectrum is generally carried out through equivalent circuits, where the basic components include: pure resistance R, with an impedance value of R; Pure capacitor C with impedance value of 1/j ω C; Pure inductance L, with an impedance value of j ω L. In actual measurement, a certain frequency is ω When a perturbation sine wave signal is applied to the electrolytic cell, the double layer can be considered as a capacitor, and the resistance caused by the electrode itself, solution, and electrode reaction can be considered as resistance. The equivalent circuit is shown in Figure 1.