I want to measure the impedance of a microbial electrolysis cell. In the literature, they usually set the initial frequency to 100 kHz however, the potentiostat we have is limited to 20 kHz. What kind of differences should I expect when I measure the impedance with a 20 kHz initial frequency instead of 100 kHz? Will I obtain accurate results?
Dear Berkan Öden ,
The frequency plays an important role in Impedance spectroscopy. The ideal theoretical circuits are drawn in order to support your claims for the best electrode. While if you see in the circuits, you will always find either a capacitor or constant phase element, which are frequency-dependent elements.
Considering a ideal Randles circuit with a resistance in parallel with capacitor
At higher frequencies: The charge can pass through the capacitor easily, while at lower frequencies: it doesn't allow the charge to pass means an infinite resistance.
So, yes, at a higher frequency, it is easier to get an EIS plot with lower Z values; at a lower frequency, the Z values are higher.
Choice is yours, but generally, to compare between different electrodes, you should use similar conditions of frequency.
Mohit
Your potentiostat is too slow to measure frequencies above 20 kHz. At high frequencies one can measure the solution resistance. Usually, 20 kHz is sufficient to measure it in aqueous solutions. If not, you can model your impedance (approximate it by an appropriate circuit) and obtain solution resistance with its standard deviation from the model (using correct weighting, e.g., modulus-model).
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