I recommend red, not green.

Your green area (potential range: Ecorr - 80 mV ... Ecorr + 80 mV) is in the

polarisation resistance region. First rule: avoid to use it.

For a Tafel plot use, the software looks for two linear segments of log|i| vs E record: you have one, only in the cathodic region (in the red area). Second rule: look for linear segments, not tangents.

Try to read this simple introduction:

https://en.wikipedia.org/wiki/Tafel_equation

Dear Bartłomiej Szwed I think you got very interesting results.

1-Surely the active region inside square 1 should consider, since the critical current density icc is more or less the value of corrosion current density icorr.

In this case the only way to solve the determination of icorr graphically is by intersect Ecorr line with the cathodic tafel line ᵦc which is appear at ideal behavior as the cathodic part of the polarization curve contain in the middle a clear straight line which is ready to extrapolated as tafel cathodic line . Meanwhile when icc is higher than iccor, the determination of icorr graphically should done by intersect Ecorr with the cathodic and anodic tafel lines ᵦc and ᵦa respectively.

2-The passive current density is always should be lower than the critical current density icc but not corrosion current density icorr since the value of passive current density ip depends on the kinetics of passivation process.

Best regards

Thank you all for the uploaded materials and above all for the tips, I will try to calculate the value in respect to square 1