Hello,

It's really difficult to help you without anyother information. Working Electrode, conditions... Are you sure about the stationnarity of your system ? Personally, I think that you're equivalent circuit is not adapted to your system.

Sorry if I'm slighty OT, but what is the name of the program that you are using? Is it available in Ubuntu repositories or did you have to compile it by yourself?

Thanks

I have attached the EIS basic notes... go through and let me know whether these files are helpful in your case...

@Stanislav Thank you!

Fitting are used to estimate the value of charge transfer resistance, solution resistance and warburg impedance.  I think your fitting is correct. Your fitting value almost matches with experimental data. 

Kotagiri, my rule of thumb is that if the relative standard error of the residuals of the fit,  is 10% or greater that is a poor fit; 3-5% probably acceptable and meaningful; and 2% or less good. Values of 1% or less are excellent. The errors on the parameters depend on the weights you use. Ideally, you should perform a weighted fitting on your data using the std due to noise as weights in order to obtain unbiased model parameters. I send you a reference where I illustrated how the user´s decision on which signal processing it is used to measure impedance affects the impedance std and, therefore, the standard error of the residuals of the fit.

http://iopscience.iop.org/1742-6596/434/1/012002