Franklin Gutiérrez Hello, I am happy to try to answer your good questions. From my experience in using electrochemistry tools, first of all, we need to define the high and low frequencies where part of our materials belong. For my case in ceramic coating material usually, the higher frequency is assigned to the outer layer (coating), and for simplifying the lower frequency is assigned to the inner layer (substrate) or we can also mention it as the interface between coating and substrate.

In the case of material coating for anti-corrosion, the assessment of electrochemical impedance spectroscopy (EIS) presented by Bode plot means that the presence of a high phase angle in high frequency corresponds to the higher corrosion resistance of the materials, especially in the outer layer. I hope it can help you to conclude your data, and here I enclosed some references that also discuss the relation between Nyquist plot, Bode plot vs Phase angle, and Bode plot vs Impedance. Thank you

I am happy to participate in this discussion.

Reactions that take place fast belong to the high-frequency domain like charge transfer and other reaction like diffusion takes place at lower frequencies. The higher frequency part of the diagram manifests the reactions corresponding to the electron transfer which might be electron transfer through the material. If the impedance is high in the high-frequency domain, that means the material regardless of how many layers it has impedes electron transfer.

Likewise, the low-frequency domain gives data about ion transfer and diffusion,, high impedance in the low-frequency area means that diffusion of ions is difficult which I believe is the double layer forms on the interface between electrolyte and material.

Typically there are semicircles (namely constant phase elements)in Nyquist plots, the equivalent circuit model, simulates a resistor in parallel with the capacitor. the capacitor means the electric double layer forms at interfaces and the resistor is the resistance of the material itself against electron transfer. since the phase angle is the phase shift between the current and voltage. there is no phase shift when V=IR but the phase angle changes when V = I Z.

As long as the double layer forms in the outer layer, the first CPE is forming, the capacitor of the layer is charging up and the phase angle is changing. Low-frequency domain lets reactions happen that need time for a movement like the diffusion of anions. indeed, diffusion of anions take place in electrolyte and throughout the coatings if coatings become permeable. So if the impedance at low frequencies is high, that means the ionic movement is not a matter of importance.

phase angle shows the phase shift between the current and voltage when the real resistance is replaced by the impedance. the high phase regardless of which frequency, means that the impedance tends to be more like a capacitor, not real resistance, to me it is like the CPE is forming there but when the phase angle is low means that the impedance resembles the real resistance instead. so the high phase angle indicates high impedance and when it happens at the high frequency it means that the material impedes with charge transfer.