As many electrochemical techniques, if you want to compare different samples with different surfaces, you have to correct the measured values by the exposed surface. for example, in electrochemical techniques, the total measured current has to be correct to obtain the current density express in A.cm-2 (for example).

Impedance is define by Z=dE/dI, so correcting current I by current density i (from surface S), we obtain dE/di = Z x S (Ohm.cm2).

So a resistance will be express in ohm.cm2, and a capacity in F.cm-2

Thus you can compare different samples with different surfaces

As many electrochemical techniques, if you want to compare different samples with different surfaces, you have to correct the measured values by the exposed surface. for example, in electrochemical techniques, the total measured current has to be correct to obtain the current density express in A.cm-2 (for example).

Impedance is define by Z=dE/dI, so correcting current I by current density i (from surface S), we obtain dE/di = Z x S (Ohm.cm2).

So a resistance will be express in ohm.cm2, and a capacity in F.cm-2

Thus you can compare different samples with different surfaces

Expressing differently what said Yannick, which is fully correct, I would say the following:

- for bulk properties, for instance the conductivity of electrolytes, you are interested by the volumic conductivity because (i) it is an intrinsical property (ii) this is the value that will be used to detrmine electrolyte resistance: R = sigma. e/S

- for electrode properties, it is different because the electrode mechanism is so complex that you can not extract an absolute parameter/value related only to the electrode material intrinsical properties. In this case, we focus thus on a property that is related to the target funcionality. For electrodes, we want the smaller resistance per area unit so this is the value we use. BUT keep in mind that this value is related to electrode materials intrinsical properties, porosity, connectivity of grains, thickness etc...

I would say that the normalization of impedance plots (Nyquist and Bode) with respect to surface area is the most reasonnable way we have found to compare electrode materials. It allows comparing performance but says very little about relevant mechanisms.

Hoping it helps.

Guilhem

In the electrochemical surface characterization step for my enzyme-biosensor study, i ve faced the same question by a reviewer. My surface properties are in accordance with the classical Randles circuit model. 

Dear Prof. Dezanneau, how can i interpret and export the normalized graph from a conventianol Nyquist plot graph (X axis: Zreal and Y-axis: Zim)? Do i change the graph with Frequence (x) to Phase Degree (Y)?

And, do you suggest a paper about this?

Bilal Demir

Dear Bilal Demir Sir,

I also faced the same question by a reviewer,  in investigation of antibiotic drug  by using nano material based biosensor. How can I normalised EIS data per area ? 

can you suggest me paper ?

I agree fully with Guilhem;

currently I´m wondering about a good methode to figure out the electrode properties for capacitive electrodes (with a thin passivation) for biosystems; electrodes used for recordings in electroactive cell culture should not interact with the medium, furthermore act as "antenna" for the field gradient. Therefore it seems to be reasonable to define a surface-related impedance (Ohm/mm²), which is actuallay a normalization regarding the electric field per area unit (V/mm²). Does someone use the same method?

Any hint, even literature would help. Heike

the following analysis show how the electrode area can affect the measured resistance R and how it is resistance can be made with reference to an electrode with area= 1 cm^2.

Assume that we have two electrodes immersed in electrolyte where the immersed cross sectional area of the twp electrodes are equal of area A. assume that the spacing between the two electrodes is L and the resitivity of the electrolyte is roh, then accordingly one can expels the resistance between the two electrodes as

R= roh L/A,

Rearranging

R XA= roh/L

From this relation it is clear that

When A =1cm^2, then it will give the properties of the electrolyte roh and its path length L.

then the correct unit is ohm.cm^2.

Best wishes

Thank you one and all for your valuable answers related to my question.