Good morning everyone. I am currently trying to perform impedance measurements on some stainless steel tubes that have been hot oxidized in a oven at 1030°C under a controlled atmosphere.
We are having a lot of troubles with the measurements, since the experimental data are really not consistant with what we are expecting. In attachment you can find an image with a comparison between a "good" measurement and a "bad" one. The problem is that the "bad" ones are way more frequent than the "good" ones.
I am using a Bio-Logic SP200 single channel potentiostat, a special EIS Ag/AgCl reference electrode, a Pt counter electrode and the working electrode is the stainless steel tube. The electrolyte is a 0.02M KNO3 solution, that is outgassed with pure N2 for 30min before the measurements. The cell is contained in a faraday cage, since we believed the bad measurements could be caused by some kind of electrical disturb. Unfortunately we did not have better results even with the faraday cage.
In attachment you can also find a picture of the experimental setup.
I thank you a lot for your help.
Hi Christian! Thanks a lot for your useful answer!
I am currently trying a measurement doubling the number of measures per frequency (the value Na in EC-Lab): I'm using a value of 6, before it was 3.
I'm using a "standard" amplitude of 10mV at the moment, but I can change it if I don't get better results.
As concerns the voltage range, I'm using -1 to +1 V while the I limit is set to "auto".
The real time update is that I still get bad data points with Na=6, I'm going to try changing the "I range".
Thanks a lot for your help!
Hey Christian, I had good results setting Na = 6 (6 measures per frequency) and I range = 1 mA. I tryed a quick measurement down to 100 mHz, now I'm going to perform a "real" one down to 1 mHz.
Thanks a lot, your help was really fundamental!
By the way, do you know the meaning of the parameter "bandwidth"? I read the the EC-Lab manual but I'm not getting it for the moment.
Hi Christian,
actually the Faraday cage is grounded, I forgot to mention it.
We were also thinking about forcing the WE to ground, at the moment we are working in the "standard" mode (advanced settings - electrode connections).
I will surely follow all your suggestions in order to optimize my measurements. (at the moment the measurement seems quite stable, luckily)
Thanks again for your precious help!
Have a nice day
Michael
Hi Christian,
I'm really sorry to bother you again, but I'm still facing problems with the points in the low frequency region.
I don't know if it can be seen from the picture of the electrochemical cell I'm using (extremely home made), but do you think this can be a problem related to the distance between the sample and the Pt counter electrode (it's the one on the right)? The reference electrode (on the left) is placed at about 4 mm from the sample.
Thanks again for your help!
Dear all,
I completely agree with all the precautions given by Punckt. May I stress that the CE should be with a high surface area Pt electrode facing directly the WE. The area ratio must be not lesser than 10:1. Good luck.
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