I recommend the freeware EIS Spectrum Analyzer (http://www.abc.chemistry.bsu.by/vi/analyser/). It's well designed, gives you a choice of 4 different fitting algorithms, and all are transparent so you're not tied to a proprietary software for the rest of your project. You might need to convert the data into text files with compatible columns, but in my opinion it's worth the extra step.

Thank you very much for your replay.

I understand that maybe one of the reasons I encounter an issue with the analysis is negative values of impedance. Therefore I can not fit a circuit easily. I also tried to find some literature regarding negative impedance values and did not encounter much information or maybe I need to improve the search.

I will examine the software.

Oriya.

A free version of EC-Lab can be downloaded at

https://www.biologic.net/support-software/ec-lab-software/

ZSim and ZFit are powerful tools for learning impedance spectroscopy

Thank you very much for your answer Jean-Paul.

We have their complete software however I am using PalmSens potentiostat and was not able to convert my files to a format that can be imported to the EC lab one (tried different text files but failed).

Dear Oriya Belous Maruani,

using the custom Import tool in EC-Lab you can import any type of data file, as long as they are .txt files and providing all the columns are properly separated by comma or space or semi-colon. You can choose the number of columns and affect each column with a variable. You can find some details in EC-Lab manual Analysis and data process. I hope this helps, Best regards, Nicolas