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Dear Wan Mohamad Ikhmal ,

1. What metal are you using ?

2. What are the pretreatments you did before EIS ? (i.e, mechanical polishing with SiC papers ...)

3. Did you check that you'are doing EIS in a steady state ? (i.e, measuring OCP before starting EIS)

Dear Dr. Benbouzid Abdelmoheiman Zakaria

The metal that I'm using is mild steel and yes I did the polishing process until I get a mirror finish.

As for doing EIS in a steady state, I already setup the procedures and just doing the regular process as I always did.

Dear Wan Mohamad Ikhmal ,

Ok, I'm not sure but I think your metal is suffering of one of the special types of corrosion (e.g., pitting corrosion) in such an agressive medium (Because of your previous experiments).

I suggest to do more polishing to your surface to eliminate the pitting sites.

Please let me know what is the problem If you find that.

Dear Wan Mohamad Ikhmal ,

I suggest also to check your connections and your Reference electrode.

Dear Wan Mohamad Ikhmal

Something is wrong with your setup. Please check connections and experimental parameters. What equipment are you using?

Good luck

From the diagram I can tell it is probably due to bad connections. You can see that the spectrum is more or less fine at high frequencies and then it shatters in the lower frequency region. If you're using a rubber o-ring seal that have a small diameter (4-5 mm) you can also experience lack of wetting of the electrode because of the air bubble between the sample and the electrolyte. Good luck!

Why not try using a new and freshly prepared sample of the same bare metal.

Dear Dr. Wan Mohamad Ikhmal,

after such a strange Nyquist plot, I would try the instrument with a "dummy cell" and then, if the result is correct, I would repeat the test trying to maintain the most stable conditions possible (checking connections, cell electrodes, their positioning, etc.).

Best regards,

Pierluigi Traverso