Hello Samuel Chijioke ,

As a starting point, can you provide more details of your electrochemical cell (i.e., what is your WE/RE/CE, is the WE modified, electrolyte type and concentration, total volume).

Which parameters did you enter for the EIS study (i.e., initial frequency, final frequency, AC voltage, DC voltage)?

I would also encourage that you check that all the cables and connections are clean and in good condition. Ensure that the physical connection from the potentiostat terminations to the electrochemical cell fixtures are reliable.

Working electrode is mild steel, you

Reference is Silver/Silver Chloride electrode

Counter is graphite.

Electrolyte is 0.5M HCl solution with plant extract (wonderful name), volume is 200ml.

Initial I used was -1.5

No final (check new pics attached)

No AC, no DC.

Cables are clean and okay because I just plotted a Tafel and it was very okay.

Thanks.

Hello Samuel Chijioke

In addition to Jules Lloyd Hammond 's very useful reply, I would suggest to use a "dummy cell" from the potentiostat manufacturer to ensure that the potentiostat is functioning properly.

Also you may want to check the reference electrode, is the frit blocked, is there a bubble present, is there enough salt?

Best regards,

Marie B.

Before explaining this abnormal impedance plot, I would like to mention that Impedance analysis works on the principal of small voltage fluctuations which cause fluctuations in current. When you perform an impedance analysis the instrument changes the voltage (5 mV) on both sides, (Number of times you change the voltage in one second is your frequency). If the potential difference between your working and references is not stable you might get abnormal impedance plots. I have observed the same plots but i realized that if the OCV of my cell is not stable it compromises the impedance analysis.

Something external is changing in your system during the analysis causing voltage to change. In my opinion, this could be one reason for this abnormal behavior.

The semi-circle results are for very simple circuits. Obviously, as is often the case, your electrochemical system is more complicated.

In your cell's case, the common P-EIS mode produces quite noisy spectra[1,2].

If the (alternative) G-EIS[2] mode, is available, then try[3] to use it, from now on.

1. https://www.researchgate.net/post/How_to_get_good_curves_in_impedance_measurement_technique

2. EIS: Potentiostatic or Galvanostatic Mode? https://www.gamry.com/application-notes/EIS/eis-potentiostatic-galvanostatic-mode/

3. A Galvanostatic imp. mode (G-EIS)[2] is, practically, an OCP free (for i_DC=0), EIS-mode.

Thank you all for the input. Will keep you updated

1. Please try the dummy cell first and check the EIS.

2. If your dummy cell is working fine, please check the cell connection. It is usual to get such kind of noisy and random spectra when you have loose in connection.

3. In case o faulty cell also you will get similar kind of EIS spectrum. Please first exclude such possibility.

Good day all, please this Tafel plot is not okay, the anodic slope is not okay. I don't get a slope value on checking for corrosion rate. And looking at the plot, am not comfortable with it. Please what could be the issue?

Dear Samuel Chijioke,

could you, please, remeasure this (Tafel plot), using a much lower rate (say, 1mV/s, or even less), in a lower V-range (-0.3V, -0.9V) ?

From the attached screenshot of your measurement, I think you are having a current overload scenario. Hence the constant current readings over such a wide range of potentials in both the anodic and cathodic directions

Increase the current range of your Potentiostat/Galvanostat.

If this persist you might wish to check your counter and reference electrodes.