Dear collegeus,
i did measure a porous electrode with potentiostatic impedance spectroscopy. I got a result with a significant semi-circle at high frequencys and a 45°-element at low frequencys, as expected.
What was not expected is the behaviour over 800 kHz. The real part of the impedance Z' increases with the frequency. I did search for an explanation for it but could find something.
Has anyone a suggestion what to look at? Please dont exclude anything, like problems with the cables to connect or anything in the experimental set-up you might come up with.
Thank you for your attention.
Sascha
Dear Mr. Kumar,
thank you for your responds. I will read your supposed article.
The measurement is reproducible in several cycles. It is stable over several measurements with some time between the measurements.
I am using a 2-electrode setup, because the system is fully determined by the anode geometry. The counter electrode is a lithium foil. I am using the highest frequency available for this frequenc analysator. Hope this helps to clarify. If other informations would be beneficial, please ask.
Greetings,
Sascha
Dear Sascha,
Since you are using a 2 electrode geometry, there could arise asymmetry in your configuration which could be geometric or electrical. For e.g. if you are using coffee bag or pouch cell or rectangular geometries the asymmetry can affect your low frequency response due to edge distortion of the field. Try using more symmetric configurations as ring or circular electrodes for your experiments.
Also, often the high frequency looping back is attributed to the inductive effects arising from the porous geometry. If this is the case you might as well calendar your electrodes for more particle to particle contact and the effects should be minimised.
Hello
I advice you to try make analize using module and phase components. Also it is known what two electrodes sheme of measurement have problem with polarisation efects.
Sascha, my first suspect is just a measurement artifact, as at this freq. range the Real res, have to decrease at low freq range, up to 10MHz, it is due to 1/iwt relaxation typical for individual oscillators (ie capacitor). It is clearly expressed for example by Cole-Cole law. The Real vs Imag is also looks very weird, pls compare the same for Cole-Cole model. Of course you may pick up relaxation from collective phenomena(excluding plasmon due to low freq), or have some strange membrane relaxation, and yes, you may easily pick up artifacts from electrode polarization as suggested by Vitaliy above, At the same time up to 10 MHz the inductive coupling should be small, so Shruti's note will work only at higher frequencies
Sascha, one option that I forget to mention is measurement-induced changes in your electrode good luck V
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