I cannot comment in general, but on impedance spectroscopy in fuel cells. Often the high frequency resistance is attributed to the membrane, the middles frequency is charge transfer resistance and low frequencies are giving information about mass transport limitation. It is quite obvious that we refer to processes within the fuel cell that a frequency dependent. Frequency is also transferable into time scales of processes. Maybe the image in the attachment helps.

Kind regards

Peter

The significance of frequency range in EIS has its analogues in other familiar domains in physics, like the : acoustics, optics, etc.  Acoustics is NOT[1] strictly musical in nature, include many applications based mainly on some multi-range freq. techniques[2]. Multi-range freq. in "optics" has similar freq. significance, an "obvious" advantage (night vision viewers, etc.).  Multi-range freq. in EIS has, actually, a similar freq. significance. We have to investigate our sample[3] near the frequency range Fj of an impedance Zj (different) mode j.  Otherwise (out of range), we can't model or "listen" a Zj-mode (clear of Zj-mode). On the other hand, we aknowledge better (most of the) different Zj-modes[4] based on the significance of frequency, like the clear listening of our favorite radio station (high quality factor of tuning).

1. musical or architectural in nature. Also: Room acoustics, Architectural acoustics

2. multi-range freq. techniques in acoustics, include also : noise control, SONAR for submarine navigation, ultrasounds for medical imaging, thermoacoustic refrigeration, seismology, bioacoustics, and electroacoustic communication.

3. https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-spectroscopy/

4. see Fig.8 in : http://www.bio-logic.net/wp-content/uploads/WP1_EIS_batteries.pdf

Thank you Dr. Wagner and Dr. Samaras for your comments. Appreciate your time. 

i may recommend you to read my paper published last year at Journal of Energy. A detailed description is provided and results obtained from extensive experimental investigations are presented. For further questions please do not hesitate to contact me.

Thank you Sir for your suggestions. I went through your paper. It sounds interesting. I loved the way you interpreted the Nyquist plot analysis. However i was wondering about the role of frequency regarding those process of diffusion or charge transfer. How can you make sense the lower frequency is related to diffusion. Also on what basis you choose your frequency range for EIS analysis?

Hi, lower frequency means higher the time...if the ions have more time then it can easily undergo diffusion...unlike at high frequency...it is difficult to undergo diffusion...thus, the charge transfer will be favored...

Dear Tejas D Raju ,

we must[1] add-on the (underestimated) electron[1-3] (and hole) diffusion, related, mainly, to metal oxide[2], and polymer[3], electrodes, apart to the (overestimated) ions' diffusion in EIS-spectra, at (regimes of) lower frequencies. EIS has been particularly important in the understanding of electronic properties related to metal oxide electrodes within energy conversion (heterojunction solar cells, photocatalysts/electrocatalysts) and storage devices(Li, and Na, ion batteries, supercapacitors)[2,3].

1. Theory of the Impedance of Electron Diffusion and Recombination in a Thin Layer https://pubs.acs.org/doi/10.1021/jp011941g

2. Electrochemical Impedance Spectroscopy of Metal Oxide Electrodes for Energy Applications https://pubs.acs.org/doi/pdf/10.1021/acsaem.9b01965

3. Influence of Electrolyte Cations on Electron Transport and Electron Transfer in Dye-Sensitized Solar Cells https://pubs.acs.org/doi/10.1021/jp211807w